List of The Big Bang Theory and Young Sheldon characters

Johnny Galecki

Leonard Leakey Hofstadter[1] (Johnny Galecki) is an experimental physicist with an IQ of 173. Originally from New Jersey, he received his PhD at age 24, spending at least some of his time at Princeton University. He shared an apartment in Pasadena with colleague and friend Dr. Sheldon Cooper until season 9. Unlike his equally geeky friends, Leonard is interested and adept in building relationships with other people. Compared to his friends, he is relatively successful with women.

The writers have toyed with a romance between him and next-door neighbor Penny since the series premiere, with their unresolved sexual tension being a major force for drama. Leonard dated Penny for most of season three. Following his break-up with Penny, Leonard began a relationship with Raj's sister Priya in season four. The two attempted a long-distance relationship after Priya moved back to India, but Leonard broke up with her in season five after she admitted to cheating on him. In season five's "The Recombination Hypothesis", Leonard and Penny start dating again.

In season six's "The 43 Peculiarity", Penny tells him she loves him for the first time. Over the next two years, they talk about marriage and each have unsuccessful proposals until the penultimate episode of season seven, when they become engaged. They get married in the ninth-season premiere, followed by a wedding redo for their friends and families since the couple had eloped. In the series finale "The Stockholm Syndrome", it is revealed that they are expecting their first child.

Leonard's family includes other accomplished scientists: his mother, Dr. Beverly Hofstadter, is a neuroscientist and world-renowned psychiatrist, his sister is a medical researcher, and his father, Dr. Alfred Hofstadter, is an anthropologist. Also, his brother Michael is a Harvard law professor.

Jim Parsons

Sheldon Lee Cooper (Jim Parsons) is a theoretical physicist, possessing a BS, MS, PhD, Sc.D., and an IQ of 187. Born in East Texas, he was a child prodigy, and received his PhD at age 16 from Caltech. He is often cold, self-centered, condescending, and immature, but is not intentionally hurtful: his conduct is generally well-intentioned, but poorly judged. He has a softer side, as he does care about his friends, and loves his family and wife Amy Farrah Fowler, though he often insults them either about their intellect levels or different opinions. In seasons 1–9, he shares an apartment in Pasadena with friend and fellow physicist Dr. Leonard Hofstadter.

He has a deep love and interest for science fiction and comic books, to the point of an obsession, and shows particular affinity for Spock from the Star Trek franchise. He refrains from any form of physical contact and exhibits a strict adherence to routines to the point of exhibiting signs of obsessive–compulsive personality disorder. Any disruption to routines distresses him enormously. A running gag has him always knocking on doors in a pattern of three knocks and one call repeated three times. In the interests of making life run on rational and predictable lines, he requires Leonard to sign a legalistic and exhaustive "Roommate Agreement", and later imposes a similar "Relationship Agreement" on Amy.

Sheldon has trouble in social settings. His commitment to his friends is often called into question, as he is known for being constantly and consistently, if unintentionally, condescending and rude. He also has difficulties lying or keeping a secret, giving himself away with wild facial tics and implausible statements. He is, however, fond of occasionally telling a joke or playing a prank, which he typically punctuates with his trademark exclamation "Bazinga!" He has a superiority complex and makes no effort to hide his contempt for other people's lower intellects, often making highly inappropriate comments.

Sheldon meets Amy Farrah Fowler in the third-season finale and starts a slowly evolving relationship with her. In the tenth season, the two move in together for a five-week experiment to test their compatibility and later decide to make the arrangement permanent. At the end of that same season, admirer Ramona Nowitzki makes a romantic overture to Sheldon, prompting him to propose to Amy. In the finale of season eleven, Sheldon and Amy get married. In the series finale, Sheldon and Amy jointly share the Nobel Prize in Physics for their work on Super-Asymmetry.

Kaley Cuoco

Penny (Kaley Cuoco), is Leonard and Sheldon's neighbor across the hallway. Originally from a small town outside Omaha, Nebraska, she was a waitress and occasional bartender at the local Cheesecake Factory until season seven, and is an aspiring actress. According to Sheldon, she is a "good-natured simpleton". She is kind-hearted, outgoing, and displays the most common sense out of all the original five main characters. She also appears to be the most street-smart. Her lack of educational qualifications (she dropped out of community college) are a constant source of disparaging comments from Sheldon.

She has dated several men during the course of the series, including Kurt, Stuart, and Zack, but her recurring romantic interest is Leonard. Leonard pursued Penny during season one and they dated briefly at the start of season two, which led to some awkwardness. They began dating again and were a couple for most of season three, but she ended the relationship after he told her he loved her and she was not ready to reciprocate. Penny and Leonard begin to date again during the fifth season. After several unsuccessful proposals from both sides, Penny realizes that her happiness is derived from her relationship with Leonard and they become engaged and later elope, upsetting their friends and families and leading to a wedding redo with their friends and families present. In the series finale "The Stockholm Syndrome", it is revealed that Penny is pregnant with her and Leonard's first child. She has a tense relationship with Sheldon, whose nerdy and obstinate personality often exasperates her, but they are ultimately good friends, helping each other in various situations. By season four, Penny also begins to socialize more with Bernadette and Amy, who frequently visit Penny's apartment, go out together, and comfort each other.

At the start of season eight, Penny pursues a career in pharmaceuticals and interviews for a job at Bernadette's workplace. She gets the job, and gradually becomes more independent, including earning a higher salary than Leonard. She reveals in season nine that she is not happy with her job, but insists on keeping it to help her eliminate her former credit card debts and secure a good financial future. In season 10, Leonard and Penny are finally living alone in apartment 4A after Sheldon moves in with Amy. In the series finale "The Stockholm Syndrome", it is revealed that they are expecting their first child.

Initially, not much is known about Penny's family, but it is mentioned in the series that her father, Wyatt (portrayed by Keith Carradine,[2]) raised her like a boy, her mother smoked marijuana while she was pregnant with her, her sister shot her husband while they were intoxicated, and her brother is a meth dealer. Her mother, Susan (Katey Sagal), and brother, Randall (Jack McBrayer), are finally seen in the first episode of season ten. Her family's last name is never revealed during the series.

Simon Helberg

Howard Joel[3] Wolowitz, M.Eng. (Simon Helberg) is an aerospace engineer at Caltech's Department of Applied Physics, who often hangs out at Leonard and Sheldon's apartment. Unlike Sheldon, Leonard, and Raj, Howard does not have a doctorate, and often gets disparaged as a result, especially by Sheldon. He defends this by pointing out that he has a master's degree in Engineering from MIT and that the equipment he designs is launched into space, unlike the theoretical work of his friends. In the fifth-season finale, Howard goes to the International Space Station on Expedition 31.

Howard lives in Altadena with his domineering, belittling, and unseen mother, who treats him like a child. While he sometimes expresses irritation at this treatment, for the most part, he appears to prefer it.[4] Howard dotes on his mother and participates in many of her daily routines. A recurring gimmick in the series is Howard and his mother communicating with each other from different rooms by yelling, a habit which Bernadette also adopts in later episodes. His father left them when he was 11, and Howard gets visibly distressed when the subject comes up. Howard fancies himself a ladies' man and attempts pick-up lines whenever a woman is present, although he drops this habit once he starts going out with Bernadette. He is Jewish, but is not serious about his faith, and does not keep kosher. However, he does observe the Sabbath and the Jewish holidays.

In the pilot episode, he speaks English, French, Mandarin, Russian, Arabic, and Persian, along with fictional languages like Klingon and Sindarin. Howard suffers from asthma, transient idiopathic arrhythmia, allergies to peanuts, almonds, and walnuts, and is prone to canker sores and pink eye. Howard dated Bernadette briefly in season three. After some difficulties, they resumed their relationship in season four, which culminated in their engagement. In the fifth-season finale, Howard and Bernadette are married on the roof of the apartment building shortly before he has to leave for Kazakhstan, where he is to be sent to the International Space Station. In season six, he finally leaves his mother's house and moves into Bernadette's apartment.[5] In the episode "The Comic Book Store Regeneration", Howard's mother passes away in her sleep while in Florida, prompting him to move back into his home with Bernadette. Stuart, the owner of the guys' favorite comic book store, also moves in.

Upon learning that Bernadette is pregnant in season nine, Howard panics about handling the impending baby, particularly earning enough money. With the help of his friends, he designs a new form of guidance system that attracts the attention of the Air Force. In "The Birthday Synchronicity", Bernadette gives birth to a girl named Halley, on Amy's birthday, who screams like Howard's late mother, Debbie Wolowitz.

In season 11, Howard learns that Bernadette is pregnant again and later in the same season in "The Neonatal Nomenclature", Bernadette gives birth to a boy named Neil Michael Wolowitz.

Kunal Nayyar

Rajesh Ramayan[6][7] Koothrappali, PhD (Kunal Nayyar) is Howard Wolowitz's best friend and another genius of the group. His name is usually shortened to "Raj". He is from New Delhi, India, and works in the physics department at Caltech, where his area of expertise is astroparticle physics. He lives in an apartment in Pasadena. As with his friends, he is mutually involved with and obsessed with science fiction and comic books in general. He is also a fan of Harry Potter and Indian music, but appreciates the Indian lullabies his mother sang and the catchiness of Hindi phrases. Raj is a Hindu and believes in karma (reincarnation), but eats beef. He is very shy around women outside of his family, and during the first six seasons of the show, found himself unable to speak to women while in their presence unless he drank alcoholic beverages, or believed he had done so.[8] When Penny, Amy, and Bernadette were around, Raj usually whispered what he wanted to say to Howard or Leonard, who then repeated or responded to what Raj said aloud. Despite this, Raj has sometimes ended up in bed with women, leaving the other characters perplexed.[9]

Unlike his friends, Raj has many feminine interests, such as reading Archie comics and Twilight and watching chick flicks such as Bridget Jones's Diary. A recurring joke in the series has people, including his parents and Leonard's mother, speculating that Raj might be gay due to his feminine interests and his close friendship with Howard, with whom he has arguments similar to those of a married couple. However, Raj has always stated that he is straight, but metrosexual. He had an infatuation with Penny, and secretly wrote love poems about Bernadette. Raj comes from a very wealthy family in India, and often communicates with his parents, Dr. and Mrs. Koothrappali, via webcam.[8] He has a younger sister, Priya.

In season six, Raj started seeing a shy and sweet woman named Lucy, who had many things in common with Raj. However, she feels too pressured when he asks her to meet his friends and breaks up with him. As of season seven, he no longer requires alcohol, drugs, or medication to speak in front of women. In season seven, Raj starts dating Emily Sweeney, a dermatologist, and their relationship becomes exclusive at the end of the seventh season. In the ninth season, he meets a bartender/scriptwriter and dates her along with Emily. However, in season ten, he mentions he is currently single. After his parents divorced, Raj's father ended his financial support and he was forced to move into Leonard and Penny's apartment. Due to friction between them, Raj moved into an apartment over Bert's garage. After starting to live on his own and learning to manage his own finances, Raj has finally started to work at the Observatory where his expertise is more highlighted. In the final season, Raj's father arranges a marriage for him with an Indian hotel concierge named Anu. They breakup when she take a job in London.

Sara Gilbert

Leslie Winkle, PhD (Sara Gilbert) is an experimental physicist who works in the same lab as Leonard. In appearance, she is essentially Leonard's female counterpart, equipped with the black-framed glasses and sweat jackets. She also has a lazy eye. Leslie had casual sexual relationships with both Leonard and Howard, considering it a completely physical reaction to her body's cycles. She is one of Sheldon's arch-enemies, due to their conflicting scientific theories, and takes every opportunity to insult Sheldon for mistreating her.

Sara Gilbert made her first appearance in the third episode of season one, The Fuzzy Boots Corollary and her final regular appearance in the finale of season three, The Lunar Excitation. Entertainment Weekly reported in January 2009 that she had been downgraded from starring status to recurring because the producers of the series were unable to come up with new storylines for the character.[10] She returned for a guest role in the 200th episode, "The Celebration Experimentation", in season nine, with her character talking briefly about how she and Sheldon have changed over the years and affectionately calls him "dumbass" again at Sheldon's insistence (due to his dislike for change).

Melissa Rauch

Bernadette Maryann[11] Rostenkowski-Wolowitz,[12] PhD (Melissa Rauch) is originally a waitress and co-worker of Penny's at The Cheesecake Factory, using her wages to pay for her graduate studies in microbiology. She is a smart, short-tempered, ruthless, and often competitive young woman who sometimes displays a sweet, nice, and friendly personality. Despite her squeaky voice, she has a darker side. A recurring joke in the series references Bernadette and her lab team handling dangerous or infectious specimens, leading to accidental byproducts or exposure to diseases, in some cases resulting in Bernadette being quarantined.

Bernadette is of Polish origin and Catholic upbringing, and was originally seen wearing a cross necklace. She frequently manipulates people, often pretending to be a friendly and good-natured individual, quickly making friends with Penny and Amy, as well as the rest of the gang. Despite her short stature, she is regarded as being somewhat intimidating, largely because of her sharp tongue, aggressive demeanor, and occasional signs of mania. In season eight's "The Locomotion Interruption", Penny interviews for a pharmaceutical sales representative position with Bernadette's boss, and secures it because she concurs with his opinion that Bernadette is kind of a bully and that they are slightly terrified of her.

Penny first introduced Bernadette to Howard on Leonard's request. During their first date, Bernadette and Howard do not find any common field of interest until they discover that they both have domineering mothers. After their third date, Bernadette declares that three dates is the threshold for deciding whether they want a long-term relationship. Blindsided, Howard hesitates initially, causing a temporary rift between them, but then impulsively proposes marriage to show her that he does care about her. Frustrated, she declines, but when he sings a heartfelt song for her at the Cheesecake Factory, she declares that it is the most romantic thing anyone has ever done for her and their relationship continues. A lengthy offscreen breakup occurs when she catches Howard engaging in cybersex, but Howard apologizes and their relationship resumes.

In her initial appearances in the third season, Bernadette does not use her high-pitched speaking voice and is portrayed as almost a dim-witted blonde by taking things literally and not understanding even the simplest of ideas. She mentions this fact in season four's "The Alien Parasite Hypothesis", where she says she is much smarter than Howard, but in order to protect his manhood, she acted dumber. In the fourth season finale, she obtains her doctorate and is subsequently hired by a pharmaceutical company (Zangen) that offers her a high salary. While preparing for their wedding in the fifth season, Bernadette is shocked and repulsed when she learns about Howard's past sexual escapades, although once again, an apology and reconciliation occurs in the same episode. They marry the day before Howard leaves for his upcoming mission to the International Space Station.

During seasons six and seven, the newlyweds deal with Howard's difficulty in readjusting to life on Earth, the struggle to keep a healthy relationship with Howard's mother, and arguments over money. In the ninth-season episode, "The Valentino Submergence", Bernadette reveals that she is pregnant, informing Howard in the next episode. She comically reveals that the baby was conceived in Sheldon's bed, much to Sheldon's chagrin. Raj learns about the baby's gender and inadvertently reveals that the child is a girl. In "The Birthday Synchronicity" Bernadette gives birth to a girl named Halley who screams like the baby's late grandmother, Debbie Wolowitz.

In season 11, Bernadette learns that she is again pregnant, while Howard is telling her Sheldon and Amy got engaged. Her doctor puts her on six months of bed rest, which makes her fond of watching detective- and criminal-themed TV shows. In "The Neonatal Nomenclature" Bernadette gives birth to a boy named Neil Michael Wolowitz (Neil for Armstrong, Gaiman and Diamond and Michael for Bernadette's father), but she insists that she and Howard call him by his middle name. In season 12, Bernadette pushes Penny in her sales career.

Mayim Bialik

Amy Farrah Fowler, PhD (Mayim Bialik PhD) is a neuroscientist and Sheldon's love interest in the series. She has a PhD in neurobiology (Bialik herself has a PhD in neuroscience), with a research focus on addiction in primates and invertebrates, occasionally mentioning such experiments as getting a capuchin monkey addicted to cigarettes or starfish addicted to cocaine.

Raj and Howard found Amy through an online dating site after secretly establishing an account using Sheldon's name and information. The site matches her to Sheldon, and the two share many similar traits. Once she and Sheldon meet, she becomes, as Sheldon puts it, a girl who is his friend, but not his "girlfriend". The two initially communicate by computer, but at the encouragement of the group, she starts socializing with the gang in person.

Early on, Amy is essentially a female counterpart to Sheldon. She is coldly rational, displays little emotion, and is awkward in social situations ranging from endearing to embarrassing. In season five, after Amy goes out on a date with comic-book store owner Stuart, Sheldon decides to solidify their relationship as boyfriend/girlfriend with a 31-page "Relationship Agreement". Later in the season, Amy begins a campaign to increase Sheldon's feelings for her by becoming more involved in his interests, including video games and Star Trek, and treating him as his mother did. Sheldon says during Howard and Bernadette's wedding ceremony that he hopes the two of them are as happy together as he is alone, hurting Amy's feelings, but he spontaneously takes her hand for comfort later as Howard is launched into space.

By the beginning of season six, they are regularly holding hands at Amy's insistence, but Sheldon repeatedly resists all of her attempts to engage in further physical intimacy. By mid-season, Sheldon gets some intimate views of Amy when he cares for her while she has the flu, pushing him further toward a traditional relationship with her. She also provides Sheldon with consoling hugs, and receives a slap on the rear by an intoxicated Sheldon who tells everyone that she is a great gal.

They eventually move into Penny's old apartment together, while Penny moves in with Leonard, and later make the arrangement permanent. Amy is later offered a three-month course at a science camp in New Jersey and leaves with Sheldon's encouragement. She becomes angry when she learns of Sheldon spending time with Ramona Nowitzki, who she suspects has romantic feelings for Sheldon (which she does). In the season finale, after Ramona kisses Sheldon, he visits Amy and proposes to her. The episode ends on a cliffhanger awaiting her answer. In the season 11 premiere episode "The Proposal Proposal", which picks up immediately after Sheldon's proposal, Amy's answer is further delayed by a phone call from Leonard and Penny, after which she finally says yes. She and Sheldon marry in the season 11 finale. Amy objects to Sheldon wanting to provide sperm for Zack Johnson's baby, but does try and get him excited about having their own child.

In the final season, Sheldon and Amy publish their work on super-asymmetric string theory and win the Nobel Prize in Physics together.[13]

In 2020, a year after The Big Bang Theory went off the air, it was revealed that Kate Micucci, who ultimately got the role of Lucy, had auditioned for the role of Amy Farrah Fowler.[14]

Kevin Sussman

Stuart David Bloom[15][16] (Kevin Sussman) runs the Comic Center in Pasadena,[17] the comic book store that the characters often visit. Stuart is characterized by his low self-esteem and loneliness, which often result in pathetic attempts to engage with women and win favor with the main cast. This is despite owning his own (albeit troubled) business, and being a talented portraiture artist who attended the Rhode Island School of Design.[18]

During Stuart's first appearances in season 2, he shows enough social skills to ask Penny on a date on two occasions, though neither ends successfully. In "The Hofstadter Isotope", his first date with Penny goes well for most of the evening, but when they return to her apartment, their run-in with Sheldon devolves into an endless argument between Stuart and Sheldon over the minutiae of Batman comics that puts Penny to sleep. In "The Classified Materials Turbulence", their second date unravels when in the throes of a romantic embrace, Penny calls him "Leonard", ending any future prospects for them as a couple. In season five, Stuart goes on a date with Amy, but Sheldon interrupts the date to solidify his relationship with her.

Stuart was the partner of Wil Wheaton in a trading-card game tournament in which they defeated the team of Raj and Sheldon. As proprietor of a comic-book store, Stuart has an almost encyclopedic knowledge of comic books and superheroes. In the season-four episode "The Toast Derivation", he mentions that he is in financial trouble and that the store is now also his home, and over the years, he has questioned the profitability or success running the store.

During "The Decoupling Fluctuation", Stuart becomes close friends with Raj and joins the gang as Howard's replacement while he is in space. When Howard returns, Sheldon wants to dismiss Stuart from the group, but Raj objects. Leonard tie-breaks on the basis that they are receiving a 20% discount in Stuart's store, and Sheldon relents after Stuart offers to go as high as 30%, thereby becoming a bigger and more prominent part of the core group. Sheldon has tried to hide his clear belief that Stuart is more of a hanger-on to the group of friends than a core member, most notably in a story where Stuart was part of a motley "test brunch" along with Burt the geologist and a neighbor who only spoke English she'd heard on TV, so Sheldon could work-out any hosting issues before trying an event with his "real" friends. Stuart actually got angry and told Sheldon it was clear they didn't even see him as a friend, leading Sheldon to sincerely apologize and try harder to be nice to Stuart for a period. Stuart is also limited vis-à-vis the group because he is a lot like Raj, a mostly-single guy around three couples, but Raj is best friends with Howard and closer friends with the others than Stuart.

After his comic-book store is destroyed in a fire, Howard offers him a place to stay and a job as his mother, Debbie's, nurse. Stuart likes the job and develops a surprising closeness with Debbie, even staying long after she recovers, to Howard's annoyance. After Debbie's death, Howard and Bernadette move back into the house, with Stuart still staying. In the eighth-season finale, the two attempt to ask Stuart to move out, but are unable to bring themselves to do it after Stuart reveals it is his birthday. He eventually makes his own decision to move in the middle of season 9; however in the middle of season 10, he reveals that he has been evicted from his apartment and tries to use his helping with Howard and Bernadette's baby to move back in with them, much to Raj's chagrin. He does not always appear with the main group, as he was somehow not at Howard and Bernadette's during the birth of their 2nd child Neil.

Kevin Sussman was a recurring guest actor from seasons two to five, and was promoted to starring role for the sixth season onwards.[19]

During season 11, he hires a woman named Denise (Lauren Lapkus), at his shop, and becomes attracted to her. In the season 11 finale, Denise is his date to Sheldon and Amy's wedding, where she exhibits an attraction to Stuart when he displays a superior level of knowledge of Star Wars trivia to Mark Hamill, who is performing the ceremony. In the second episode of season 12, they are revealed to have made out at the ceremony, and have their first date at the end of that episode.

Emily Sweeney, M.D., (Laura Spencer) is a dermatology resident at Huntington Hospital, whom Raj finds on an online dating site. Emily went to Harvard and is shown to have a slightly alarming personality trait: she delights in the macabre.

In season seven, after finding Emily's online dating profile, Raj has Amy contact her. Amy and Emily exchange emails and find they have a lot in common. Emily does not like Raj's inability to correspond with her directly; but, when he does agree to meet her, he acts weirdly and she leaves. Raj later bumps into Emily and apologizes for their previous encounter. She gives him another chance and agrees to go out to dinner with him. In "The Relationship Diremption", Raj and Emily have dinner with Howard and Bernadette. Upon meeting Emily, Howard recognizes her from a blind date they had sometime before he met Bernadette. The blind date ended badly, causing him embarrassment at the dinner, but no issues.

In "The Gorilla Dissolution", Raj and Sheldon bump into Emily at the movies with another guy. Later, she visits him to talk and reveals that the guy was her tattoo artist who had been asking her out for weeks and she did so just to end the obligation. Emily then spends the night; and, in the next episode, Raj reveals to the gang that Emily and he are exclusive.

In season eight, Raj introduces Emily to Leonard and Penny; however, Penny senses that Emily does not like her. Emily reveals that she is uncomfortable with the fact that Raj and Penny previously kissed. Emily and Penny later sit down to settle their differences, with mixed results. Emily continues to socialize with the gang in season 8, and in the finale, she suggests to Raj that they have sex in a graveyard. Raj wonders whether he should break up with her because of her alarming personality. The next season, Raj somewhat rashly breaks up with Emily after meeting another girl, Claire, and fantasizing about starting a family with her, though Claire makes amends with her boyfriend and berates Raj for his actions. He tries to reconcile with Emily, but she shuts the door in his face. Later in the season, Emily and Raj reconcile after a tearful phone call. However, in season 10, Raj mentions that he is currently single. He and Howard invite Emily, Claire, Lucy, and Emily the deaf woman to Raj's apartment for an intervention to find out why women keep dumping Raj. Emily mentions that, although she enjoyed her sexual relationship with Raj, she was put off by his fear of his parents.

Laura Spencer was a recurring guest actress on the series in seasons seven and eight. During production of season 9, she was promoted to a "fractional" starring role; the upgraded status ensured her availability on an as-needed basis, without requiring her in every episode.[20] She returned as a guest in season 10; the character was written out of the series, and did not appear after season 10.

Mary (née Tucker)[21] Cooper (Laurie Metcalf) is Sheldon's loving, caring and religious mother and a devout Christian from Texas. She has two other children besides Sheldon--Sheldon's twin sister, Missy, and his brother George, who is shown via a family tree to be three or four years older than Sheldon and Missy. Her husband, a rambunctious alcoholic, was also named George, but he died when Sheldon was still a boy. To Mary's relief, her other children do not share Sheldon's hyperintelligence, once commenting to Leonard, "I thank the good Lord my other kids are as dumb as soup". Mary herself is not intellectual, but is quite wise, though she is prone to making insensitive comments such as calling Japanese words "kung fu letters" at a sushi restaurant, or calling Native Americans "our" Indians. Despite her religious views, she is tolerant of other faiths, as evidenced by her serving Raj a dish of chicken after making sure it was not something Indians considered "magical". She also struggles to follow her beliefs sometimes. She is a loving mother and has been able to control Sheldon, with Leonard describing her as Sheldon's "Kryptonite" to Penny. When Penny and Sheldon engaged in a fierce dispute, Penny called for Mary's help, who subsequently called and scolded Sheldon about his actions.[22] Leonard wishes his mother were as loving as Sheldon's mother, although Sheldon himself appears at best ambivalent about her parenting. Sheldon mentions that Mary once hit him with a Bible because he refused to eat his Brussels sprouts. She apparently thought something was wrong with her son while he was growing up, as Sheldon will often remark after someone calls him crazy, "I'm not crazy; my mother had me tested!" Though Mary confirms this, she wishes that she had taken him to Houston for further testing.

In her first visit, Leonard calls Mary to intervene when Sheldon is fired for being disrespectful to his new boss, Dr. Gablehauser. She manages to convince Sheldon to apologize and he gets his job back, and she becomes romantically interested in Dr. Gablehauser. When Sheldon asks, "Is Dr. Gablehauser going to be my new daddy?", Mary replies, "We'll see".

In season three of The Big Bang Theory, after returning from the North Pole, Sheldon returns to his home in Texas after the other guys tampered with his research. Mary calls the guys and they come to fetch Sheldon. Sheldon initially refuses to leave, although after an argument with his mother about evolution, Sheldon decides to leave. Mary is again called to intervene in "The Zazzy Substitution" when Sheldon buys a clowder of cats after his "break-up" with Amy. Mary uses reverse psychology to get Sheldon to reconcile with Amy. She again comes to visit in "The Rhinitis Revelation" before going on a Christian cruise, and Sheldon becomes jealous when she would rather go sightseeing with the rest of the gang instead of cooking for him and attending physics lectures.

In season seven of The Big Bang Theory, Sheldon returns to Texas to assist Mary in the birth of his twin sister's baby. Howard later takes Sheldon to see Mary after visiting NASA headquarters, but flees after Sheldon sees her having sex. Sheldon returns and gets into an argument, and is sent to his room. After Howard tells him about how he drove away an admirer of his mother, Sheldon apologizes to Mary, saying that he will accept her choices on the outside while condemning her internally for being a hypocrite by going against her religious beliefs. Mary forgives him.

In season 8 of The Big Bang Theory, Mary meets Dr. Beverly Hofstadter, Leonard's mother. The two very different women start out as civil, but later quickly clash as Beverly insults and belittles Mary's strict religious beliefs, and Mary in turn derides Beverly's cold attitude. Mary is especially insulted when Beverly is left dumbstruck how a genius intellect like Sheldon could be born to a woman like her. After taking a break from each other, the two come to terms: Mary decides to forgive Beverly for her offhandish ways, and Beverly realizes there is more than one way to raise a child. The two mothers make up and Beverly tries unconditional love by trying an awkward hug with Leonard.

In season nine of The Big Bang Theory, Sheldon calls her to tell her that Amy broke up with him and that he would like to send the family heirloom engagement ring back, but she advises him to hold on to it, just in case. She reappears in the season finale "The Convergence-Convergence" where she comes to attend Leonard and Penny's re-wedding where she is not at all happy to see Beverly. She meets Leonard's father Alfred Hofstadter and the two get along great as they have each other's nice, gentle, and caring personalities, bonding over their mutual dislike of Beverly, and their admiration of each other's beliefs. The two of them end up fighting with Beverly at the restaurant during the pre-ceremony dinner and the two leave together and after finding out they are staying at the same hotel, they decide to share a cab and it is implied that the two hook up.

In season 10 of The Big Bang Theory, during a visit to see her, Sheldon and Amy break it to her they are living together and Sheldon is stunned that she is not offended that they are "living in sin" due to her belief he was never going to find anyone.

In season 11 of The Big Bang Theory, Mary reappeared in the season premiere, "The Proposal Proposal", when Sheldon phoned her to tell her that he and Amy were engaged. Mary was happy for both of them, but she was not surprised, as she had been praying for them. Sheldon informed his mother that they would not be getting married in a church, which was okay with Mary, as she said anywhere Jesus is a church, and he'll be there in her heart. She was also quite surprised to hear that there was more than one woman interested in Sheldon, otherwise she might've prayed a little too hard. After hanging up, Mary thanks the Lord for making the engagement happen, and that even though he (the Lord) can do anything, that was mighty impressive.

She reappeared in "The Solo Oscillation", where she called Sheldon, who was annoyed by it, since he was trying to find something to work on.

In "The Bow Tie Asymmetry", Mary and her daughter Missy are picked up from the airport by Raj. She mentions that they had also been driven to the airport by an Indian fellow. Missy object to her comment. Mary also is in denial that her daughter is also separated from her husband. Later at the wedding, when Mrs. Fowler wants to take her daughter way because she thinks that Sheldon has left her at the altar, Penny tells her to stop and that Sheldon would never hurt the woman he loves. Mary stands up and applauds Penny who tells her to sit down too. Mary also tells Sheldon how proud she is of him and that her comment that sometimes it is the imperfections in things that make things perfect gives Sheldon an epiphany about his string theory work.

Mary has argued with Leonard's mother, Beverly, over the fact she never nurtured Leonard properly the way she has with Sheldon, while Beverly has criticized her for her narrow-minded beliefs.

A younger version of Mary (played by Metcalf's real-life daughter Zoe Perry) is a main character in the prequel series Young Sheldon. It is revealed in season 2 that Mary became a devout Christian after a difficult birth with Sheldon and Missy where Missy almost died. It is also revealed that she had a miscarriage after the pregnancy with Sheldon and Missy. In season 3 it is revealed that she was forced into a shotgun wedding with George.

George Cooper Sr. is the father of Georgie, Sheldon and Missy Cooper and the husband of Mary Tucker-Cooper. In The Big Bang Theory, it is established that he died when Sheldon and Missy were fourteen years old. He is portrayed by Lance Barber, who previously portrayed Jimmy Speckerman in one episode of The Big Bang Theory.

George "Georgie" Cooper Jr. (Jerry O'Connell): Sheldon and Missy's brother, who lives in Texas and runs a car tire business. Often at odds while growing up, the Cooper brothers begin to reconcile their differences when Sheldon and Leonard visit George in season 11 before Sheldon's wedding. Known as Georgie in his younger days, he appears as a main character on Young Sheldon played by Montana Jordan.

Missy Cooper (Raegan Revord): She is intellectually and socially quite unlike her brother.

The adult version of the character is played by Courtney Henggeler and appears in the episode "The Porkchop Indeterminacy" of Big Bang Theory. Missy has grown up to be a tall, attractive woman that promptly catches the attention of Leonard, Howard, and Raj. Sheldon realizes that, within Missy's eggs, lies the potential for another "superior mutation" like him. He temporarily sets himself up as a guardian to Missy in order to choose the best mate for her. Missy refers to Sheldon as "Shelly" and, despite their differences, she loves him and is proud of his accomplishments. In "The Cooper Extraction", she gives birth to a baby boy with Sheldon helping while her husband is recovering from a motorcycle accident, but does not appear on-screen. Henggeler reprises the role in the eleventh-season finale "The Bow Tie Asymmetry", where Missy, pregnant with her second child, travels with her mother to Pasadena to attend Sheldon's wedding. It is mentioned that she is separated from her husband, which piques Raj's interest.

June Squibb

Constance "MeeMaw" Tucker[21] (June Squibb): Sheldon's grandmother from Texas. Sheldon is her favorite grandchild, whom she calls "Moonpie". Sheldon, in turn, is very affectionate and protective toward her; while he can be very critical of other family members, he will not allow anyone to criticize his grandmother. Meemaw is often mentioned by Sheldon, but did not appear on the series until episode 14 of season nine, "The Meemaw Manifestation".

Meemaw takes an immediate dislike to Amy upon meeting her. It appears she came to visit her grandson, but the real reason she came was to size Amy up and she dislikes Amy because of her breaking Sheldon's heart when she broke up with him. Meemaw keeps this to herself until dinner where she reveals this in front of her grandson, his girlfriend and the married Hofstadter couple. Later, Sheldon reasons with her about how she made her husband (Sheldon's maternal grandfather) a better person when he was stubborn and egotistical and Meemaw soon gives her blessings to Sheldon and Amy's relationship.

In the prequel series Young Sheldon, Meemaw is played by Annie Potts. In that series, it is revealed that she is Sheldon's maternal grandmother and has a significant gambling habit.

Jeffery Difford (Matt Hobby) is a pastor at the church that Sheldon and his family attend in Young Sheldon. Like Mary, he has friction with Sheldon's atheism, but he often challenges Sheldon to explore their line of thought through logic exercises. He was originally given the last name Hodgkins, but it was changed to Difford as of the episode "Seven Deadly Sins and a Small Carl Sagan".

Margo Harshman

Alex Jensen (Margo Harshman) is a Caltech graduate student who appears in season six. Sheldon hires her to review his kindergarten and elementary-school notebooks for any possible Nobel Prize-winning research and attend to the tasks that Sheldon perceives a waste of his own valuable time. Amy is at first jealous until she sees Alex instead flirting with an unresponsive Leonard.

After repeated attempts by Alex, Leonard finally realizes that Alex is making advances toward him. While proclaiming his loyalty to Penny, Leonard is flattered. Sheldon interferes (with the perceived intention of mitigating a situation that needed none) by lecturing Alex, but only succeeds in insulting her. After Alex files a sexual harassment complaint, Sheldon is forced to apologize and is ordered take a university-mandated online sexual-harassment course. Because Sheldon considers his own time as too valuable to waste on it, Sheldon asks Alex to take the course instead. For Valentine's Day, Sheldon sends Alex out to buy a present for Amy, which he likes so much, he keeps.[24]

Anu (Rati Gupta) is the woman who Raj's father sets him up with after asking him to arrange a marriage for him who first appears in season 12. She works in a hotel as a concierge.

In "The Wedding Gift Wormhole", depressed over everyone else being in a relationship, Raj asks his father to arrange a marriage for him, and sets him up with Anu. On their first date, Anu's commanding personality and practical approach to marriage startle Raj but nonetheless he agrees to go ahead with it. Howard criticizes Raj for this – he never expected Raj to just give up on romance. Raj admits this to Anu so she proposes to him, and he says yes. She meets Penny and Bernadette in "The Tam Turbulence", where they track her down at the hotel she works at to check her out and end up impressed by her connections in the hotel industry, although the evening turns sour when they get drunk and end up telling her embarrassing things about Raj. In "The Consummation Deviation", Anu wants to have sex with Raj for the first time, but he gets so nervous that his selective mutism returns. Confessing this to her, she is very understanding, revealing an unusual secret of her own: she hates music. The next morning, he is able to have sex with her in the shower. When Raj installs a doorbell camera at Anu's home, he accidentally spies on her and sees her greeting her ex-boyfriend, they realize how little they know about each other. The wedding gets cancelled, but they agree to start their relationship over by just dating. Anu later gets a job offer while working in London, and Raj considers leaving to propose to her, but Howard convinces him to wait for the right woman.

Bob Newhart

Arthur Jeffries, or Professor Proton (Bob Newhart) is the star of a fictional in-universe science show that Sheldon and Leonard watched as children. The character is a homage to Mr. Wizard.[25] After the show was cancelled, Jeffries was not taken seriously as a scientist and resorted to doing children's parties as his persona. In "The Proton Resurgence", Sheldon hires him to do a private party for Leonard and himself (and Penny). Later, Jeffries has a heart attack as a result of climbing the apartment stairs with his equipment. He asks Sheldon to take his place at a party for a Korean family, which Sheldon agrees to do as "Professor Proton, Jr".

While Sheldon idolizes him, Jeffries is constantly irritated by Sheldon's personality, and takes a shine to Penny. In "The Proton Displacement", Leonard, Sheldon, and Amy bump into Jeffries at a drugstore, and Sheldon becomes upset when Jeffries asks Leonard for help on a paper instead of him, and when he finds out that Jeffries thinks he is annoying, Sheldon works with Bill Nye the Science Guy, whom Jeffries accuses of stealing material from his TV show. After Nye abandons Sheldon and files for a restraining order against him, Jeffries arrives at Sheldon and Leonard's apartment and asks Sheldon for his advice on his paper (although Sheldon already hacked his email account and read it for himself).

In "The Proton Transmogrification" on Star Wars Day, Leonard tells Sheldon that Jeffries has died. Sheldon immediately pretends not to care and refuses to go to the funeral. Jeffries appears to Sheldon in a dream, where Sheldon compares him to Obi-Wan Kenobi, dressing him in Jedi robes and making him appear as a Force ghost. When Sheldon asks for his wisdom, Jeffries tells Sheldon to appreciate everything in life, including his friends, and never take it for granted.

Jeffries returns in "The Opening Night Excitation" when his ghost convinces Sheldon to spend time with Amy on her birthday instead of going to see Star Wars: The Force Awakens as he had planned to do for months. After hearing Professor Proton's words, Sheldon decides to prove his devotion to Amy by finally having sex with her, as she has been hoping he will do for the past few years. Some time later, after Sheldon takes Amy to see The Force Awakens, Jeffries returns to Sheldon to ask him about his first sexual experience with her, but Sheldon thinks Jeffries is talking about the film and tells him he enjoyed it.

For his role as Jeffries, in 2013, Newhart won his first Primetime Emmy Award. Newhart plays the same character on Young Sheldon.

John Ross Bowie

Barry Kripke, PhD (John Ross Bowie) is a co-worker of the guys, who frequently clashes with Sheldon. He works in plasma physics. Kripke has a case of rhotacism in which he pronounces the letters "R" and "L" as "W" in much the same way as Elmer Fudd from Looney Tunes, Jimmy Five from Monica's Gang and Gilda Radner in her "Baba Wawa" sketches. In season five, Kripke purchases an iPhone with voice-recognition technology, but, because of his rhotacism, the device is incapable of understanding his verbal "wequests", prompting him to deride it as ineffective. Until season seven, whether he was aware of his impediment was never clarified.

In his first appearance, he pits his robot, the Kripke Krippler, against the men's robot, M.O.N.T.E., in an unofficial robot fight.[26] The guys lose to Kripke, and M.O.N.T.E. is destroyed. In "The Friendship Algorithm", Sheldon attempts to befriend Kripke to gain access to an open science grid computer to conduct research, but it turns out to be futile, as Kripke has no control over the computer's usage time, and Sheldon consequently expels Kripke from the group.[27] Kripke continues his antagonism towards Sheldon in "The Vengeance Formulation" by pulling a prank on Sheldon when he is a guest on NPR's Science Friday by putting a helium tank in his office, making Sheldon's voice more squeaky, though Sheldon takes revenge by humiliating Kripke in front of the President of the University and the board of directors.[28] In "The Toast Derivation", Sheldon tries to befriend Kripke and a few others when he is feeling excluded by his friends, but Kripke and the others all connect in a manner that Sheldon finds 'wrong' and leaves.[29]

In season five, Kripke and Sheldon battle over a retired professor's office; but, after a long sports contest, Kripke loses to Sheldon. He is later invited to Howard's bachelor party, where he uses his turn toasting to complain that no strippers are at the party.

In season six, Kripke and Sheldon are forced to work together on a proposal involving fusion reactors, which involves an exchange of work. Sheldon is shocked to discover that Kripke's work is more advanced than his own, and he tearfully admits as much to Amy. Kripke assumes that Sheldon is in a sexual relationship with Amy and that has led to his work quality declining, and Sheldon does not deny it (although this appears to be just a convenient excuse since his work is inferior to Kripke's). Kripke also battles for tenure alongside Sheldon, Leonard, and Raj.

In season seven, Kripke ridicules Sheldon when his discovery of a new element was false, nicknaming Sheldon "The Retractor".

In season nine, Kripke calls Sheldon and Amy's live show Fun with Flags along with Raj and directs the conversation to irrelevant questions to the show. He also uses the show to call out for potential romantic relationships and asked Amy questions about her love life when Sheldon and she broke up. He attends Sheldon's birthday party and constantly hits on Leonard's mother, Beverly.

Brian Posehn

Professor Bertram Kibbler (Brian Posehn) is a geologist at Caltech, who met Amy while she was working there in her own lab in "The Occupation Recalibration". Bert brings Amy interesting and beautiful rocks every day. It takes Howard and Raj to point out that he likes her. Bert then asks her to a rock and mineral show, which she declines because she has a boyfriend. When Bert starts talking about how no one wants to do anything with him, Amy in a fit of sympathy agrees to go. Unfortunately, Bert is taking it as a date. Raj and Howard offer to talk to him to let him down easy, and they end up going with him to the show.

Bert first appeared in "The Contractual Obligation Implementation" where he is socially awkward and Raj meets just prior to a library date with Lucy. He tried to crash their date, and Raj sent him away. His name was not mentioned in the plot, but the closing credits gave the name Bert.

In "The Dependence Transcendence", Bert hosts a Caltech party that only Amy and Penny attend. He feels that Amy is the coolest girl at work and that Sheldon is cool only because he is dating Amy. As the girls are leaving, he tells them that he is in love with both of them.

He reappears in "The Fetal Kick Catalyst" as a guest at Sheldon and Amy's brunch in their apartment. He mentions that a girlfriend he was living with once moved out and took all his best rocks.

In "The Geology Elevation", Bert wins the MacArthur Fellowship grant, which makes Sheldon jealous. When Sheldon finally confronts him over this, Bert points out that the theoretical physicist has his friends and Amy to be happy about. In his office, his diploma shows he received his degree from the University of Arizona. He later accompanies Sheldon to The Ellen DeGeneres Show to make peace. His full name is shown in his award. By the end of season 10, Raj moves into the apartment over Bert's garage.

Bert reappears in "The Separation Agitation", and it is revealed that he has a recent girlfriend named Rebecca, who only appears to be with him for his grant money. After breaking up with her, Bert instantly regrets it and buys expensive gifts to win her back. At the end of the episode, he is revealed to have succeeded.

Christine Baranski

Beverly Hofstadter (Christine Baranski) is Leonard's narcissistic, unloving, and overly analytical mother. Beverly is a neuroscientist, as well as a psychiatrist. She is Sheldon's female equivalent regarding neurotically strict speech patterns, lack of respect for social conventions, and compulsive attention to detail. The only reason she had children was to use them as personal experiments for her research, so was very distant and unmotherly towards Leonard. Beverly mentions that Leonard's brother and sister are more successful in their respective fields than he is; though she respects this enough to keep contact with them (unlike Leonard), she is not proud, since they are not her accomplishments. One of her famous books is Needy Baby, Greedy Baby, in which she describes an infant's (Leonard's) unrealistic nurturing expectations. Sheldon often refers to her books when frustrated with Leonard's attempt to obtain some of his personal needs in their relationship. Leonard sees his mother as cold and not nurturing, even telling Penny that one time he made a hugging machine just to get hugs (and that his father asked to borrow it). The lack of Beverly's maternal feelings and actions toward Leonard has led to him being called the "King of Foreplay" because of his obsessive need to please.

In her first visit, Beverly makes Penny cry by delving into her history with her father (driving her, and later Leonard, to the bottle), and considers Raj and Howard's relationship to be an "ersatz homosexual marriage". After bonding with Sheldon, Beverly sings Journey's "Any Way You Want It" with him on karaoke.

In season three, Beverly comes to visit at Christmas, where she reveals that she is divorcing her husband, Alfred, after she caught him in bed with another woman. Despite Leonard's reluctance to tell Beverly about his and Penny's relationship, Penny takes her to the Cheesecake Factory for a round of drinks and reveals their relationship. After Beverly gropes a busboy, she and Penny both go to Del Taco and then return to Leonard and Sheldon's apartment where she confronts Leonard on not telling him about Penny, and then is confronted by him for not being a loving and caring mother for him. After Beverly tries to show motherly affection by hugging Leonard, she kisses a shocked Sheldon and leaves. The next morning, a hungover Beverly gives her blessing to Leonard and Penny's relationship and vows not to reveal her drunken kiss with Sheldon, wanting to work instead on her maternal relationship with Leonard.

In season five, Sheldon calls Beverly on Skype to help Leonard following Penny and Raj's hook-up, and she tells Leonard to "buck up, sissypants...If you need any more help from me, my books are available on Amazon".

In season seven, Leonard uses Beverly's latest book to get sympathy from Penny. However, Bernadette finds out from Howard what Leonard is doing and tells Penny, who calls Beverly, leaving a briefly pantsless Leonard to chat with his mother on Skype. Leonard later informs his mother of his engagement to Penny, but she reveals that Sheldon already told her. She decides to accept his engagement with Penny because Sheldon likes her.

In season eight, Beverly comes to visit to see Leonard receive an award, where she meets Sheldon's mother, Mary. The mothers get into an argument after Beverly describes Mary's religious beliefs as a superstition, and Mary, in turn, berates Beverly for her cold and distant attitude towards Leonard. Beverly later reflects with Sheldon that perhaps other ways exist to raise children than she did. The mothers make up and Beverly tries to show affection by hugging Leonard, though it is awkward for both of them.

In season nine, she attends Sheldon's birthday party and enjoys a proposition from Barry Kripke. Later, she returns for a visit to interview people for her new book, and spends her time bonding with Amy and Bernadette, frustrating Penny's attempts to bond with her. When Penny confronts her for this, she admits that she feels insulted about not being invited to her son's wedding. Penny suggests doing a second wedding ceremony for her, which she accepts and the two finally bond. She is unhappy about her ex-husband, Alfred, attending since their marriage ended due to his affair, and is even angrier when Alfred and Mary Cooper display mutual attraction and leave the rehearsal dinner together. Beverly and Alfred argue all night and Beverly once again quarrels with Mary. At the ceremony, she agrees with Alfred that Leonard was the best thing to come out of their relationship.

In season 11, Beverly begins talking to Penny as a friend and confidant, troubling Leonard, especially when he learns that Beverly told Penny that she is proud of her, a level of praise she never bestowed upon Leonard himself. When Leonard confronts Beverly, he is touched when she says that of all of her children's spouses, Penny is the one she is most impressed by, and that for this, she is indeed proud of him.

She reappeared in "The Novelization Correlation" as the character Ilsa from Leonard's book, as well as appearing over Skype.

In season 12, she appeared in "The VCR Illumination" via video chat when Leonard and Penny talked to her about comforting Sheldon. She reappeared in the seventeenth episode, "The Conference Valuation".

In "The Maternal Conclusion", Beverly visits Leonard and Penny acting nice and truly interested in Leonard's new physics project. Later she admits that she is doing research for a new book which makes Leonard blow up. Finally he forgives her which makes both of them feel much better and they end in a true loving embrace.

For her role as Beverly, in both 2009 and 2010, Baranski was nominated for an Emmy Award for Outstanding Guest Actress in a Comedy Series.

Alessandra Torresani

Claire (Alessandra Torresani) is a writer for a children's science fiction series whom Raj and Howard meet in the comic book store in season 9. Claire wants to collaborate with Raj on the science portions of a movie script. When Raj reveals to her that he has a girlfriend, Emily, she assures him that she is only interested in his technical assistance, and they can still meet as friends. However, Raj develops visions of marriage and children with Claire. After Raj breaks up with Emily, he calls Claire on Valentine's Day, only to learn that she has just got back together with her boyfriend. She also calls Raj an "ass" for breaking up with Emily just before Valentine's Day. Later, however, she asks Raj out for a drink after she has again broken up with her boyfriend. However, Raj is on his way to reunite with Emily, and chooses to be with her. However, Raj later starts seeing Claire again while at the same time dating Emily. She and Raj continue to date, but they keep their relationship casual with no commitment. When she meets Raj's friends, Claire begins to realize that Raj has been dating multiple women, and successfully tricks him into admitting it.

In season 10, Raj reveals that he is now single, having broken up with both Emily and Claire at the ladies' behest. Later in the season, when Raj tries to figure out what is wrong with himself, Claire accepts an invitation to Raj's apartment, where she meets his previous girlfriends. Claire reveals that she broke up with Raj after finding him too needy and vain and declares that she is now in a better relationship.

Stephen Root

Dan (Stephen Root) is a senior member of staff at Zangen, who first appears in "The Locomotion Interruption" when he interviews Penny for a pharmaceutical sales representative position as a favor to Bernadette. Penny realizes that the interview is not going well so she ends it and starts to leave. As a favor, she asks Dan not to tell Bernadette how badly she did because she is kind of scared of her. Dan says that he thought he was the only one who was scared of her. They start to bond, agreeing that Bernadette is something of a bully. Dan comments that she has that squeaky little voice, and that everyone else thinks she is SO nice. He had to cut one of Bernadette's research programs, but was too scared of her to do it. Dan and Penny both agree not to tell Bernadette about the results of the interview. Later Bernadette is talking to Howard at home, and tells him that it is hard to believe, but Penny got the job. She feels that it is because Dan really loves her.

Dan reappears in "The Champagne Reflection", when Penny makes Bernadette face up to her bullying ways. Dan is still afraid of Bernadette, and tells the story of how she yelled at him and his grandson after they lost the three-legged race at the company picnic. His grandson called her the mean kid with the big boobies. Bernadette is horrified when she realizes how everyone perceives her. Her father had taught her to be tough and she can be cruel with some of her comments without even knowing it. She says she thought she was the sweetest person she knew, and should be in a tree baking cookies like a Keebler elf. She goes to apologize to Dan and discovers that, owing to everyone's fear of her, they have been paying for her daily coffee even after the company stopped doing so (something they accomplished with a swear jar kept for Bernadette's sake); and have given her the private use of a toilet that was meant for everyone. She now feels like she has to leave the company and starts crying. Desperate for her to stop, Dan promises to keep paying for her coffee, and even offers to get her an espresso machine. Bernadette has found a new way to get what she wants.

Stephen Merchant

Dave Gibbs (Stephen Merchant) is a tall British man who dates Amy after she breaks up with Sheldon. Dave is recently divorced because his wife left him for a French chef. When her friends try to find Amy a date on a dating mobile app, they see a text message from Dave, and Amy reveals they have already gone out together for coffee. Sheldon is about to propose to Amy for closure when he sees Amy and Dave kissing after their date. When Amy and Dave later go out again for dinner (while Penny, Bernadette, and a reluctant Leonard spy on them), he shows an unusual fascination with Sheldon, which discomforts Amy. He considers Sheldon and Leonard to be physics superstars and idolizes them. He later gets an opportunity to meet Leonard and shake his hand after Leonard has to relieve himself while spying on their date, and with great excitement, Dave announces that he will never again wash his hand. After Sheldon rejects Amy's proposal that they be a couple again, Amy once again tries dinner with Dave, who goes out of his way to refrain from mentioning Sheldon, knowing how uncomfortable that subject made her previously. Sheldon then suddenly arrives and professes his love to Amy, and the two mend their relationship, leaving Dave to awkwardly excuse himself and invite Sheldon to meet again on his way out.

Lauren Lapkus

Denise (Lauren Lapkus) is the assistant manager at Stuart's comic book store introduced in season 10. She is quite a comic book geek. At first, Sheldon doesn't like the change that her hiring brings to the store, but starts to like her because of her comic book knowledge and her ability to figure out his preferences in comic books. After being annoyed by Sheldon's praising of Denise, Amy goes down to the bookstore to demand that Denise teach her enough about comics to make it appear that she likes them. In "The Bow Tie Asymmetry", Stuart asks her to come to Sheldon and Amy's Wedding with him. Denise declines until she learns that Star Wars actor Mark Hamill is going to be there. She sits beside Stuart at the wedding and watches as he answers questions about Star Wars better than Mark Hamill. Denise is amazed by his knowledge and calls him hot. A relationship starts between Denise and Stuart in "The Wedding Gift Wormhole". They spend time together and enjoyed each other's company though Stuart is insecure about their relationship. Denise invites Stuart to move in, but he backs off not wanting to ruin their relationship. In episode twenty-two of season 12, "The Maternal Conclusion", they move in together after convincing Denise's creepy roommate Mitch to move out.

Eric Gablehauser (Mark Harelik) is the head of the Physics Department, the group's boss at the university. When he first starts working at the university, he fires Sheldon after Sheldon insults his intelligence. Eventually, Gablehauser rehires Sheldon after he and Sheldon's mother display a mutual romantic interest. Gablehauser later hosts the Physics Bowl,[30] and gives Raj attention when he is featured in a People article for discovering a planet.

Brian George

V. M. Koothrappali (Brian George) is Raj's father in India. His wife and he communicate with their son via Skype and constantly try to arrange dates for him. They want their son to marry a woman of Indian descent and give them grandchildren.[8] Although in many episodes Raj mentions that he grew up in poverty, his friends remind him of the contrary by pointing out that Dr. Koothrappali is a gynecologist, drives a Bentley, and employs servants.[31] In one such episode, Raj replies that the Bentley is leased and there are only four servants in his family home, two of whom are children. Dr. Koothrappali enjoys Doogie Howser reruns, which are apparently new to India.[8][31] Other than Raj, he also maintains contact with their daughter Priya via Skype whenever she is out of India. In season four, Dr. Koothrappali becomes angry with Leonard when he learns that his daughter, Priya, is dating Leonard without his knowledge. According to Sheldon, the Koothrappalis are "Richie Rich rich".

The Koothrappalis go through a rough patch in their marriage, culminating in them separating in season eight around the time of their 40th wedding anniversary, with Dr. Koothrappali moving out and Mrs. Koothrappali setting fire to his car. Dr. Koothrappali makes his first physical appearance on the show in season eight, visiting the main characters at a Christmas party after the divorce. Dr. Koothrappali later cuts off Raj financially when he buys a helicopter drone, but Raj manages to turn the situation around by pitting his father against his mother. He also asks his father to give advice to a nervous, pregnant Bernadette.

In "The Allowance Evaporation", Raj after meeting his ex-girlfriends who said he was too spoiled and a momma's boy, tells his father that he was no longer taking any money from him. His father was delighted that his last only unmarried offspring was going to stand on his own two feet.

In "The Wedding Gift Wormhole", it's revealed that he is dating again and decides to set up Raj with a woman for an arranged marriage.

He returns in "The Propagation Proposition" via video chat after Raj has broken up with Anu; he is angry about any money he has lost due to the wedding being cancelled.

Alice Amter (left)

Mrs. Koothrappali (Alice Amter) is Raj's mother in India. Mrs. Koothrappali is especially worried that, despite Raj being old enough to marry, the closest they have to a daughter-in-law is "that little Jewish boy Howard".[32] She enjoys Doogie Howser reruns, which are apparently new to India.[8][31] Other than Raj, she also maintains contact with Priya via video chat whenever she is out of India. She also had some anger towards Leonard when it became apparent that he was dating Priya without her knowledge.

Following their divorce in season eight, Raj mentions that his mother bought the book Eat, Pray, Love and used it to set fire to her ex-husband's car. Mrs. Koothrappali makes her first physical appearance on the show in "The Graduation Transmission", where Raj uses the Koothrappali's divorce to get money from her when his father cuts him off financially, and pits her against her ex-husband.

Regina King

Janine Davis (Regina King) is a human resources representative working at the university. She first appears in season six after Sheldon offends his assistant Alex while trying to solve a problem regarding her crush on Leonard, leaving Mrs. Davis to handle Alex's sexual-harassment complaint against Sheldon. Sheldon tells Mrs. Davis his belief that she, like all women, is a "slave" to her sexual "urges", unaware that his remarks are racist and sexist. In his attempt at defense, Sheldon rats out what he considers similar behavior by Raj, Howard, and Leonard, prompting Mrs. Davis to summon them to her office, as well. Mrs. Davis later serves on the tenure committee that is considering Raj, Sheldon, Leonard, and Kripke for a vacant tenured position, causing each of them to try to win her favor. Sheldon, in his effort to earn the position, offends her once again by giving her the box set for the miniseries Roots. Despite this, Sheldon is still short-listed for tenure, even if he offends Mrs. Davis yet again by giving her what he thinks is a traditional handshake originating in African American communities.

In season seven, Mrs. Davis says that she is recently divorced because her husband cheated on her, and Raj attempts to strike up a conversation with her at a university mixer. After offending her, Raj apologizes, and the two talk about their troubles. Following the mixer, while Raj is insistent that Mrs. Davis and he had a "moment", Howard disagrees. Mrs. Davis makes another appearance in season 8, where she informs Sheldon that he has to teach a class as a junior professor, and in season 11, has to deal with Leonard after he gives an embarrassing interview on the radio about the university.

Kurt (Brian Patrick Wade) is a tall, intimidating bodybuilder and Penny's ex-boyfriend at the beginning of the series. In the pilot, Penny reveals that he cheated on her, and Leonard and Sheldon later go to his apartment and attempt to retrieve Penny's television set from him, but they were unsuccessful and Kurt apparently found them so irritating that they returned home without pants.[33] Kurt is invited to Penny's Halloween party, for which he dresses up as a caveman, where he has yet another run in with Leonard, who is dressed as a hobbit. After Kurt sees Penny kissing Leonard, Leonard victoriously shouts to him, "That's right, you saw what you saw. That's how we roll in The Shire!"[34]

In season two, Penny experiences financial difficulties. After Leonard learns about Penny's problems, he tries to help her cut expenses, and in the process learns that Kurt owes her $1800. Without telling Penny, Leonard and the guys go to Kurt's place to collect the money, but they are unsuccessful, and Kurt writes "I owe Penny $1800 ~ Kurt" on Leonard's forehead in indelible ink. Later, Penny reveals that Kurt visited her the next morning and paid her, in turn. However, much to Leonard's disappointment, Kurt never told Penny about Leonard's visit, and instead took the opportunity to ask Penny out for dinner.[35] However, the date apparently does not go anywhere as Kurt is never seen or mentioned again.

Kate Micucci

Lucy (Kate Micucci) shows up at a party at the comic-book store on Valentine's Day at an event for people who had no dates. She has social anxiety issues, which allows Raj and her to connect. On their first date, she becomes so nervous that she goes to the bathroom and climbs out of the window to get away. Raj falls apart and refuses to leave his apartment; however, after apologizing to him, Lucy and Raj start afresh. Raj and Lucy have a date at a library and communicate by text messages, and at the end, she offers to kiss him, but chickens out at the last second. In "The Bon Voyage Reaction", Raj tries to introduce Lucy to the rest of the gang. Lucy becomes nervous at the thought of meeting so many new people that Raj suggests she meet just one of his friends first, to which she agrees. Lucy meets Amy, but Raj pressures Lucy and upsets her. Lucy breaks up with Raj by an email, and afterwards a heartbroken Raj finally speaks to Penny without having consumed alcohol. Originally, Kate Micucci had been one of the actresses considered for the Amy Farrah Fowler character.

In season seven, Penny meets Lucy at the Cheesecake Factory and confronts her about her breakup with Raj, and later Lucy arranges to meet with Raj to apologize to him for breaking up with him via email. This leads Raj to believe the two of them will get back together, but Lucy tells him she is with someone else. Although she is not seen, Lucy later texts Raj saying that she misses him and wants to get back together, but after finding out that he is also dating Emily, Lucy rebuffs Raj.

Lucy appears in season 10, where Raj invites her to his apartment along with his other ex-girlfriends to find out why he is still single. Lucy mentions that she is now in a better relationship.

Mike Rostenkowski (Casey Sander) is Bernadette's father and a tough retired police officer. Mike has a rough and rude personality and often bullies others, although he deeply loves his daughter, calling Bernadette his "little girl". Before he is first seen, Bernadette establishes his personality by telling Howard a long list of subjects he cannot discuss with Mike, including Jimmy Carter, foreigners, homosexuals, and even Howard's Jewish identity.

In his first appearance, he tells Howard that, while he does not think highly of him, his respect for Howard grew when he learned he had been selected to become an astronaut. However, after Howard expresses his fears about not returning from space, Mike tells him not to worry as Bernadette will have no trouble finding another suitable bachelor if Howard dies in space, much to the future astronaut's dismay. In the season-five finale, Mike attends Howard and Bernadette's wedding and walks his daughter down the aisle.

In season six, Howard and Mike are pushed into a fishing weekend by their spouses, but neither man really wants to go. Mike suggests that they go to a casino to shoot craps. Having earned more of Mike's respect, Howard is now able to address him as "Mike" rather than "Sir".

In season seven, because his wife is out of town, Bernadette gets Mike to come to Howard's mother's house for Thanksgiving dinner, though he would rather watch football at home. Since Sheldon understands football from growing up with his father, Mike and Sheldon bond and drink heavily together. After insulting Howard, Mike later tells Howard that he is not "all that bad", but implies that this statement is untrue when he comments on his drunken state. In "The Table Polarization", Mike, Bernadette, Raj, and Mike Massimino (via Skype) perform an intervention on Howard's decision to go back to space. Mike mentions that Howard asked him to shoot him in the foot to avoid the first space mission, which Howard insists was a joke.

In season nine, he comes to Howard and Bernadette's house since they are talking about renovating and he comes over to help. While Howard and he are busy under the foundations of the house, Mike asks Howard why he does not want kids, but Howard sets things straight when he tells Mike that it is actually Bernadette who does not want kids. In the room above, Bernadette overhears this and tries to drown out the conversation by yelling "Earthquake!" and drumming her feet on the floor, causing a dust avalanche on both of them. Bernadette had lied to her father about not wanting kids because she did not want to disappoint him. Mike says he does not want to see her miss out since raising children was the most rewarding experience of his life, but Bernadette points out that her mother did everything while all Mike did was come home from work, sit on the couch, and drink beer, which is unrelated to raising kids. Defeated, Mike leaves, saying this is really a conversation for husband and wife and tells Bernadette if her mother asks, he was at the Wolowitz house until 10. He briefly comes back into the kitchen and sees Howard and Bernadette doing "dirty talk" and then disappears again through the doorway.

Joshua Malina

President Siebert (Joshua Malina) is the president of the California Institute of Technology. He is married and has a daughter. Siebert is often mentioned by Sheldon. A recurring gag is that Sheldon often calls or visits Siebert in the middle of the night to get information, and usually gets a bitter response. Siebert sends Sheldon on the expedition to the North Pole at the end of season two.

In his first appearance, Siebert organizes a get-together with wealthy donors and faculty members to garner funds for the university's programs. He urges the guys to make an appearance to schmooze the donors so they will give to their projects. Seeing Sheldon's behavior toward the donors, he asks that he not appear again.

In season five, Siebert forces Sheldon to use up his vacation days, and when Sheldon and Kripke battle for an office at the university, they interrupt Siebert at a urinal to get him to make a decision on who gets the office.

In season eleven, the President returns and is very excited about Sheldon and Amy's asymmetry string theory paper. He helps them promote it and submits a Nobel Prize nomination for the two of them.

Priya Koothrappali (Aarti Mann) is Raj's younger sister. Having graduated at the top of her class at the University of Cambridge (where like Sheldon, her roommate was from Texas), she is one of the lead attorneys at India's biggest car company.

In her first appearance, Priya has a two-day layover and comes to visit her brother. Leonard and she are revealed to have had a relationship five years earlier (without her parents' or Raj's knowledge) when she was in town, and that Leonard had been much more invested in the relationship than she was. Leonard even offered to relocate to New Delhi to be with her. He tries to keep their relationship a secret from the guys, but Sheldon discovers Priya in their apartment after spending the night together. Leonard eventually reveals to the rest of the guys that he spent the night with Priya, as he is unable to bear the burden of keeping the secret.[36] Priya returns to Los Angeles for business in "The Cohabitation Formulation", and Leonard and she decide to try to have a real relationship, over the protests of Raj. It upsets both Raj, knowing that his sister is having sex with one of his best friends (sometimes in Raj's bed), and Penny, who is revealed to harbour unresolved feelings for Leonard. Priya soon becomes jealous of Penny and asks Leonard to stop spending time with her, which causes Penny, Amy, and Bernadette to hate her. Priya contests Sheldon's roommate agreement with Leonard, employing her legal background to deny Sheldon power over him, but upon Amy's advice, Sheldon drafts a new agreement and blackmails Leonard into signing it by threatening to tell Priya's parents she is dating Leonard, which she cannot bear because they want her to date an Indian (although her father would accept her dating Howard due to his belief that Jews are financially savvy and do not drink much). At the end of season four, Leonard overhears her parents claiming that she is moving back to India, which he interprets as the end of their relationship, leading him to expose their secret relationship to her parents.

In season five, although they are separated, with Priya moving back a month earlier than expected, they nonetheless remain in touch via Skype, having a cyber-dinner/breakfast date. At Howard's suggestion, Leonard and Priya also attempt to simulate intercourse, but when it comes time for her to remove her clothing, Leonard's screen freezes up because of his exceeding the bandwidth. Leonard later manages to get cue cards to help himself with a seduction speech to Priya, but while delivering it to her, he inadvertently reveals to her parents that they are cyber-dating (they were in the same room as she when he called), with them acidly asking for him to continue with the speech.[37] In "The Good Guy Fluctiation", Leonard tells Priya about his attraction to a comic-book enthusiast named Alice; Priya admits to cheating on him with her former boyfriend, which visibly upsets Leonard. When Priya states that they both messed up a little, Leonard retorts that while he messed up a little, she messed up a lot.[38] She claims that it is not a competition, to which he replies that it is and that she won and he switches off his laptop. In the next episode, Leonard refers to himself as single, indicating that Priya and he have broken up as a result of their last conversation.

In season 10, it is mentioned that out of the six Koothrappali children, only Raj is still single, indicating that Priya has married since her last appearance.

Riki Lindhome

Ramona Nowitzki, Ph.D., (Riki Lindhome) first appears in the season 2 episode, "The Cooper–Nowitzki Theorem", when she is a graduate student at Caltech who is a huge fan of Sheldon's work and develops a near-obsessive crush on him. She meets Sheldon personally in the cafeteria and arranges to have dinner with him in his apartment. Where other people might be worried about such behavior being reminiscent of stalking, Sheldon reacts positively to Ramona by appreciating the fact that he is getting a free dinner. During their date, the rest of the gang is sitting on the couch as spectators of this strange turn of events. She keeps "helping" Sheldon by arranging suitable working conditions for him, such as getting breakfast for him at the cafeteria and giving him foot rubs. Unfortunately for Sheldon, she overdoes her insistence that Sheldon dedicate his time solely for work, depriving him of his favorite hobbies such as playing games, watching TV, and going for paintball with the guys. Even more unfortunately for Sheldon, he cannot seem to get rid of her, especially when she settles herself in his apartment. Ramona proves to be irritating for the entire group, especially when she assumes that Penny likes Sheldon. She still asks Penny to be sisters with her. She makes it difficult for anyone to communicate with him and scares them away. Eventually, Sheldon solves the problem he has been working on. Enthusiastic about his solution, he asks Ramona how he can reward her for all her help. But when she asks for him to share credit with her and name the theorem "Cooper-Nowitzki", he finally kicks her out of the apartment.

Ramona reappears in the season 10 finale. She now has her Ph.D., and has secured a post-doc position at Caltech. Amy is away at Princeton, and the gang becomes worried for Sheldon because Ramona's crush on him begins again. She brings him meals, and eventually kisses him in his office. Finally aware of her advances, Sheldon makes an excuse to leave the office, and promptly flies to New Jersey where he proposes to Amy.

In the first episode of season 11, Amy shocks Ramona by hugging her, as it was Ramona's advances that prompted Sheldon to propose.

Ruchi (Swati Kapila); is a new co-worker of Bernadette's at Zangen who first appears in season 11. Ruchi used to live in India, and was in an arranged engagement, until she broke off the engagement and moved to America.

In her first appearance, Bernadette takes Ruchi out for drinks, though despite Howard's suggestion, refuses to set her up with Raj or Stuart. While out for drinks, Raj and Stuart show up uninvited (after Howard told them where they were) and both take an interest in Ruchi and try to win her over. Raj invites Ruchi out for drinks behind Stuart's back in a bid to get her alone. When Stuart shows up and later throws Raj under the bus, she tells them that she is not interested in dating anybody right now and just wants to make some friends. Raj later bumps into Ruchi at a bar while watching a cricket match with Howard and they eventually hook up. Afterwards, Ruchi wants to keep things casual with Raj, which he has difficult maintaining, especially after a date with her when she reveals that she does not believe in soul mates and sees romantic love more as a bio-chemical reaction. Despite this, Raj continues to see Ruchi to have sex with her. While she is on bed rest, Bernadette becomes convinced that Ruchi is trying to steal her job and asks Raj to investigate her suspicions. After revealing to Raj she is taking over all of Bernadette's projects, Raj tells Bernadette and tries to defend Ruchi like a boyfriend would, pointing out Bernadette's hypocrisy as she would most likely have stolen from other people's projects as well. When she finds out about this, Ruchi is not happy and promptly dumps Raj.

Wil Wheaton, who plays a fictionalized version of himself

Wil Wheaton plays a fictionalized version of himself. Wil played Wesley Crusher in Star Trek: The Next Generation, a character that Sheldon idolized as a child. In 1995 Wheaton made Sheldon's "mortal enemy" list after Wheaton failed to show up at a fan convention. Sheldon took a 10-hour bus ride to attend the convention and was disappointed that Wheaton was a no-show.

In season three, Sheldon enters a trading-card game tournament (Mystic Warlords of Ka'a) to confront Wheaton. When Sheldon is about to defeat his hated rival, Wheaton tells him that he missed the 1995 "Dixie Trek" convention because his grandmother had died. In sympathy, Sheldon deliberately messes up his next move to benefit Wheaton. Wheaton reveals that he lied about his grandmother and then wins the game by taking advantage of the opening Sheldon leaves him. Wheaton later plays in a bowling match against Sheldon, where he uses gamesmanship again, breaking up Leonard and Penny to win.

In season four, Wheaton appears at a special screening of Raiders of the Lost Ark and uses his celebrity status to go to the front of a long line. This antagonizes Sheldon, who derides him as the "Jar Jar Binks of the Star Trek universe". Wheaton and his entourage effectively prevented Sheldon and his friends from attending the screening when the last seat in the theater went to the person directly in front of them in line. Ultimately, Sheldon steals the reels containing the prints of the film and Wheaton leads a mob of angry audience members after Sheldon.

In season five, Wheaton invites the guys to a party at his house and appears to be genuinely sorry for his past actions, giving Sheldon a signed Wesley Crusher action figure as a way of thanking Sheldon for being a fan. His gesture is met with a renunciation of his "mortal enemy" status and a hug from Sheldon. Wheaton is invited to Howard's bachelor party, where he films the toasts and uploads them to the Internet, getting Howard and Raj in trouble with Bernadette.

In season six, Wheaton appears in a Star Trek-themed episode of Sheldon's web-series Fun with Flags and insults Amy after she criticizes his performance. After Sheldon ditches Amy to spend time with Wheaton, Amy becomes angry with Sheldon, who later unknowingly becomes intoxicated and almost starts a fist fight with Wheaton, demanding an apology.

In season seven, Amy calls Wheaton to cheer up Sheldon after Leonard disproves Sheldon's scientific discovery. Wheaton later gives Penny advice when she wrestles with whether to take a role in the sequel to a low-budget horror film in which she once starred. After taking the role, Penny finds that Wheaton is also appearing in the film. Wheaton and Penny are both fired from the film after an argument with the director.

In season eight, Wheaton invites Penny to appear on his podcast, where she talks about her acting career. Leonard and Penny get into an argument on air, much to the amusement of Wheaton.

In season nine, Wheaton introduces Adam Nimoy, son of Mr. Spock portrayer Leonard Nimoy, to Sheldon, for Sheldon to be interviewed for a documentary that Adam Nimoy is producing about Spock and his impact on popular culture. In a later episode, Wheaton fills in for Sheldon when he joins Leonard, Howard, and Raj for the midnight premiere of Star Wars: The Force Awakens. When he arrives at the theater, the audience immediately jeers him for dressing as Spock, but Wheaton explains that he did so intentionally because he believes the audience should not take whether the film succeeds or fails so seriously. He appears again to celebrate Sheldon's birthday in the show's 200th episode, "The Celebration Experimentation".

In season eleven, Sheldon wants to replace Arthur Jeffries in the role of Professor Proton, following Jeffries' death, and asks Wheaton to be his acting coach for the part. However, when Wheaton somehow gets the part instead, Sheldon is dismayed and after many unsuccessful attempts to get his friends to boycott the franchise, he demands that Wheaton turn down the role. Wheaton refuses, claiming he wants to inspire young scientists and Sheldon begins to consider him an enemy again. However, after watching the show Sheldon likes Wheaton's portrayal of Prof. Proton and gets jealous when he sees that Wheaton has brought Howard to be a guest on his show. Although Sheldon apologizes to Wheaton, mending their friendship, Wheaton refuses to bring Sheldon as a guest on his show and instead invites Amy to be a guest on the show. At the end of season eleven, Wil is Sheldon and Amy's first choice to officiate their wedding ceremony, but is replaced when Mark Hamill becomes available.

In season twelve episode "The D&D Vortex", Wheaton as Professor Proton invites Sheldon to meet William Shatner, and Sheldon gets so excited that he then proceeds to throw up on him. When Sheldon shows up at Wheaton's house to apologize, Wheaton accepts the apology, but as he is in the middle of a private Dungeons & Dragons game featuring William Shatner, Kareem Abdul-Jabbar, Kevin Smith, Joe Manganiello and Stuart, he shuts Sheldon out. When the guys find out about the game, they get Stuart to quit and Wheaton invites Leonard, asking him not to tell anyone. Leonard then tells Penny and she tells Amy and Bernadette; the girls stalk Wheaton in an attempt to get themselves invited when they hear that Manganiello from Magic Mike will be there. Because of that indiscretion, Wil kicks out Leonard and admonishes the guys for using him for his connections, and says that one of the worst things about being a celebrity is not knowing whether someone will like him for himself. To apologize, the guys invite Wil to play D&D with them at Leonard's apartment, but Wil, secretly in the middle of a game with Penny, Amy and Bernadette and the group, politely turns them down but offers to arrange for another time. Penny sits next to Shatner telling him he tells "Grandpa Jokes" and Bernadette tells Abdul-Jabbar how she and her father used to watch him, while Amy creeps out Manganiello and is moved away from him. Wheaton then allows them all to take a photo together and send it to the guys as payback, which Leonard himself admits they all deserved.

Wil Wheaton, LeVar Burton, Leonard Nimoy (in voice-over only), Brent Spiner, William Shatner and George Takei have all appeared on the show, making the Star Trek franchise the most represented franchise on the show in terms of guest appearances.

Marissa Johnson (Lindsey Kraft) is married to Penny's ex-boyfriend, Zack Johnson. They meet with Leonard and Penny and they want Leonard to father their child since Zack is infertile.

Mrs. Debbie[39] Malvina[40] Wolowitz (voiced by Carol Ann Susi) is Howard's over-protective, controlling, belittling, but loving and caring stereotypical Jewish mother. The character is not shown on-screen with the exception of one episode in season six in which her body, but not face, is briefly shown. Mrs. Wolowitz's raspy voice is heard usually in scenes at her house, which she shares with Howard. She talks to Howard always by yelling at him from another room, which results in awkward conversations with Howard yelling back at her. In a flashback, when the guys hear her yelling in a masculine voice, they ask Howard if that was his father, to which Howard replies, "If she grows any more hair on her face, yes".

Mrs. Wolowitz is also described as being enormously obese and wearing a wig and painted-on eyebrows. She seems to be oblivious to Howard's work as an engineer and treats him as though he is still a child. She is a master at Wheel of Fortune and guessing answers at game shows. She frequently refers to Leonard, Sheldon, and Raj as Howard's "little friends" (as in, "I made some cookies and Hawaiian Punch for you and your little friends!") and often refers to Caltech as a "school". Howard often makes references to his mother as being a "crazy old lady", but deep down, he is deeply attached to his mother and quite happy to be treated like a child. She is also noted to be on hormone replacement therapy, and she wants to "play doctor" with Raj when he asks to sleep over.

When Howard reveals that he has proposed to Bernadette and she has accepted, she collapses, causing Howard to panic and dislocate his shoulder while trying to barge into the bathroom to help her. The timing leads him to believe that she may not like Bernadette (who is Catholic) and has suffered a heart attack from the shock of the news. In actuality, her fainting was due to food poisoning from the food she ate while meeting Bernadette and was completely unrelated to Howard's news. She has graciously accepted Bernadette as her daughter-in-law and is impressed by Bernadette's doctorate.

In an early episode, Howard attempts to move out after a fight with his mother, but has serious delusions that she is trying to force him to stay, when in actuality, she is urging him to move out, which leads to him staying. However, at the beginning of season six, she is so angry and upset about Howard moving in with Bernadette that she cries at the thought of being lonely, prompting him to promise he will convince Bernadette to move into their house instead. However, Bernadette remains firm but once Howard has finally moved out of his mother's house, he tells her a story about inviting his mother to be an assistant during his magic tricks as a child, helping her forget her loneliness, making Bernadette feel guilty and decide that she and Howard should sleep over at his mother's house from time to time to remind her that she is not alone. Later in the season, Howard asks Raj to look in on his mother to make sure she is okay while he and Bernadette are out on a trip. Raj enjoys dinner with her but as he is about to leave, she cries at being lonely, causing a sympathetic Raj to stay for dessert. He ends up sleeping in Howard's old bedroom, but once Howard warns him that his mother will use her loneliness and mother him in a desperate attempt to make him stay, he attempts to escape but is caught by her.

In season seven, Mrs. Wolowitz breaks her leg and keeps driving away the nurses hired to care for her. Even Penny rejects the job of caregiver after a very short time. After Stuart's comic-book store burns down, Howard invites Stuart to work for Mrs. Wolowitz; however, they develop a strange relationship, much to Howard's annoyance. Howard is also upset about the fact that now she dotes more heavily on Stuart, getting him premium cable, new clothes, money to rebuild the comic book store and even recording an answering machine message with him.

Following the death of Carol Ann Susi, producers decided that Mrs. Wolowitz would die in the season-eight episode "The Comic Book Store Regeneration". Howard receives a phone call while in the store from his aunt Gladys in Florida, whom Mrs. Wolowitz had gone to visit. She says that Mrs. Wolowitz lay down for a nap and never woke up afterwards. Howard and Bernadette then move back into Howard's old home, and Stuart decides to stay with them. He eventually moves out halfway through season nine, allowing them to redecorate. Mrs. Wolowitz is also in the season-eleven episode “The Bitcoin Entanglement”, using archive recordings from previous episodes.

Keith Carradine

Wyatt (Keith Carradine) is Penny's father. He comes to visit, and Penny feels compelled to involve Leonard in a ruse to make him think they are still together. (Wyatt reveals that he favors the successful Leonard over Penny's other "loser" boyfriends.) When the plot is revealed, he gets mad at Penny and feigns anger at Leonard, but after Penny leaves the room, he encourages Leonard to keep trying to get Penny back (because he wants his grandchildren to "grow up in a house without wheels"). Strangely, though, in the first episode where Leonard's mother visits, Penny tearfully reveals her rough childhood, saying that Wyatt wanted a boy and even called her "slugger" until she reached puberty. Wyatt appears again in season nine, when Penny finally plucks up the courage to tell her father she eloped with Leonard. Wyatt is happy, but he also confesses that he killed Penny's pet pig a year ago. In the season 10 premiere, "The Conjugal Conjecture", he comes to Pasadena with his wife and son to attend Leonard and Penny's re-wedding and during the ceremony he walks Penny down the aisle, welcomes Leonard to their family and advises him not to lend Penny's brother any money.

Zack Johnson (Brian Thomas Smith) is a dim-witted but friendly beefcake type whom Penny dates on and off after her second break-up with Leonard. Zack works as the menu designer for restaurants that are owned by or which have hired his father's company to design their menus.

In season three, Leonard invites Penny and Zack up to the roof to watch his experiment of bouncing laser beams off the moon; Zack misunderstands what is happening, and thinks they are going to blow up the moon.[41] Later, Penny and Zach go out to a party, but she is so put off at how stupid he is that she runs back to Leonard for sex, saying he ruined her ability to tolerate stupid men.

In season four, Zack runs into Penny, Bernadette, and Amy at a restaurant, and Amy becomes physically attracted to him. Sheldon arranges a meeting between Zack and Amy to satisfy her "urges", but his lack of intellect immediately discourages Amy. Unlike Penny's other boyfriends, Zack considers Leonard, Howard, Sheldon, and Raj (whom he calls "the science dudes") to be "cool" and makes a genuine effort to get to know them, even treating them as his friends. After accompanying them on a trip to the comic-book store (where Raj and he bond over a mutual fondness for Archie comics), he enters a New Year's Eve costume party with them, portraying Superman in their version of the Justice League. In "The Toast Derivation", Sheldon invites him over for a party, where he bonds with Kripke and Stuart, as well.

In season seven, it is discovered that Zack and Penny have been unknowingly married for three years after the two were intoxicated and attended a wedding chapel in Las Vegas (they were not aware that weddings in Las Vegas are real). Penny invites him to Mrs. Wolowitz's house for Thanksgiving, where they get the marriage annulled.

In season nine, episode 22, Zack's observations indicate he is, in some respects, more observant and smarter than "the science dudes".

In season ten, episode 22, Zack and his fiancée, Sarah, plan a double date with Penny and Leonard, but Sarah does not turn up. Zack offers Penny a job at his menu printing company which she accepts, but when she calls Zack he tells her that Sarah is uncomfortable with them working together.

In season eleven, episode 9, it is revealed that seven years prior, Penny gave Zack Leonard's old laptop, which Leonard had given her while they were dating. Penny and Leonard arrive at Zack's apartment to retrieve the laptop, where he shows them that Penny had made a video she intended to send to Leonard apologizing for their break-up.

In season twelve, episode 12, Penny runs into Zack again after he buys her, Bernadette and Amy drinks. He reveals that he has sold his menu company and become rich from the profits, and invites her and Leonard to dinner at his yacht with him and his new wife, Marissa Johnson. Penny and Leonard proceed to make fun of the newlyweds on how dumb they are until Zack and Marissa ask Leonard to be their sperm donor in hopes of conceiving a child. Because Penny said that she never wants children, Penny and Leonard argue about the situation, but eventually Penny agrees to support whatever decision Leonard makes. In season twelve, episode 15, Leonard ultimately cannot go through with it and tells Zack to ask Sheldon, whom declines after Amy is outraged at the idea.

Billy Sparks (Wyatt McLure) is a boy who lives with his parents and sister next to the Coopers and Meemaw. He has been mentioned in The Big Bang Theory as one of Sheldon's childhood bullies, although in Young Sheldon he is rather good-natured and at times is friends with Sheldon, but is shown to be extremely dim-witted and simple-minded.

Brenda Sparks (Melissa Peterman) is Billy Sparks's mother who works at the bowling alley frequented by Meemaw. She is not a very pleasant person and often clashes with Mary.

Coach Dale Ballard (Craig T. Nelson) is the owner of a sporting goods store and a part-time baseball coach who lets Missy play after he says no and Meemaw intervenes. He also ends up dating Meemaw after her breakup with Dr. Sturgis. He ends up hiring Georgie as a salesman and in the penultimate Season 3 episode, fires him after Georgie accidentally let the store get robbed even if Georgie paid him the money back; the reason of firing was to get back at Meemaw because she refused to marry him. In the Season 3 finale, Meemaw is really angry with Dale for firing Georgie and in the end of the episode grandmother and grandson get revenge together by throwing eggs at Dale’s store.

Dr. John Sturgis (Wallace Shawn) is a physics professor at the university East Texas Tech that Sheldon attends part-time. Dr. Sturgis is initially a pen pal of Sheldon Cooper, before the child prodigy audits his quantum chromodynamics course. Dr. Sturgis is instantly smitten with Sheldon's Meemaw and they begin dating, much to Sheldon's approval, but also to Sheldon's urging.

He is also rather childish like going to bed at 7:30 and asking Meemaw's permission to do things as if she were his mother.

Herschel Sparks (Billy Gardell) is a neighbor of the Cooper family and Meemaw, the husband of Brenda Sparks, and the father of Billy and Bobbi Sparks. He runs his own garage, where he offers Georgie a part-time job. Georgie turns out to be a wonderful employee, something that makes George and Herschel happy and stunned. Herschel is often bossed around by his wife, something that he and George bond over since George is often bossed around by Mary as well.

Paige Swanson (Mckenna Grace) is a 10-year-old child prodigy whom Sheldon meets in one of his classes with Dr. Sturgis. She turns out to be a bit smarter than him and this causes Dr. Sturgis to pay attention a lot to her, something that makes Sheldon jealous, so Meemaw has to step in. Unlike Sheldon, she is very sweet, has excellent social skills, and is capable of being friends with non-intellectuals, as is reflected in her friendship with Missy. When her parents divorce, she becomes mean, snarky, mouthy and rebellious. She has also changed her appearance, turned to shoplifting, grown indifferent to her schoolwork and doesn’t want to be smart anymore. Dr. Sturgis advises Sheldon to listen to her problems and so he does and this results in Sheldon learning to listen. He attempts to console her by making her a hot beverage.

Robin (Mary Grill) is a police officer and Pastor Jeff’s second wife. Pastor Jeff meets Robin in “A Broken Heart and a Crock Monster” when she stops him for passing a red light. She takes an interest in him and because of that, refuses to give him a ticket.

They begin dating and they are going pretty strong. They eventually get married in “A Live Chicken, a Fried Chicken and Holy Matrimony” and in “A House for Sale and Serious Woman Stuff” they move in across the street from the Coopers and reveal that they’re going to have a baby.

Tam Nguyen (Ryan Phuong – YS / Robert Wu – TBBT) is a Vietnamese-American boy who, in Young Sheldon, is Sheldon's classmate and only friend. His father Le Nguyen, and mother Trang Nguyen, run a store called "Medford Mart". He has two sisters, Mai and Kim-Ly.

Tam laments his difficult childhood in war-torn Vietnam, which included his father being incarcerated in a detention camp, and his encounter with the Ku Klux Klan when he first arrived in America. Tam takes his frustration out on other people, such as Sheldon's father George. He has a troubled relationship with his parents, having been treated badly by both of them after moving to the United States. The episode "A Loaf of Bread and a Grand Old Flag" suggests that Tam has a good relationship with his sisters, as he talks about starting a labor union with them and taking their parents to court.

By the time of The Big Bang Theory, Sheldon and Tam are no longer friends. In the Season 12 episode "The Tam Turbulence", they met up again after not speaking in 20 years. When Leonard, Howard and Raj find out about Tam, having never previously heard of him, they try to meet him. They do so at Caltech, assuming that Sheldon was to blame for the end of the friendship. It turns out that when Sheldon was moving to California he had asked Tam to move there with him; Tam agreed, but after meeting a girl named Beth decided to stay in Texas instead. He and Beth married soon after and had one son and at least one other child. Sheldon and Tam make up at the end of the episode, with Tam saying that he was confident Sheldon would make other friends and be successful, and that he has been happy with Beth and their children all these years and has had a very happy life overall, in contrast to his abusive childhood.

Veronica Duncan (Isabel May) is Georgie Cooper's most significant love interest on Young Sheldon.

Initially introduced as a popular and "easy" girl, Veronica becomes a devout Christian after going through a "Sin House" one Halloween. Georgie is obsessed with her and frequently takes every advantage he can to be close to her or impress her in any way, such as agreeing to be baptized with her (only to attempt – comically and painfully unsuccessfully – to steal a kiss), defend her against an abusive step-parent (after Mary had taken her in), or coming up with a series of get-rich-quick schemes to buy her expensive gifts (which she rejects, though she seems more receptive towards a bracelet made of the candy he was selling in his latest scheme).

A handful of Hollywood celebrities as well as famous scientists and engineers have made appearances on the show as themselves. In most cases, the appearances are brief cameo appearances. These appearances are in contrast to Wil Wheaton who, as described above, plays a character on the show which is a fictionalized version of himself.

• Kareem Abdul-Jabbar: "The D&D Vortex"
• Buzz Aldrin: "The Holographic Excitation"
• LeVar Burton: "The Toast Derivation", "The Habitation Configuration", "The Champagne Reflection"
• Ellen DeGeneres: "The Geology Elevation", "The Laureate Accumulation"
• Nathan Fillion: "The Comic Book Store Regeneration"
• Carrie Fisher: "The Convention Conundrum"
• Ira Flatow: "The Vengeance Formulation" (voice only), "The Discovery Dissipation", "The Retraction Reaction"
• Neil Gaiman: "The Comet Polarization"
• Bill Gates: "The Gates Excitation"
• Sarah Michelle Gellar: "The Stockholm Syndrome"
• Summer Glau: "The Terminator Decoupling"
• Brian Greene: "The Herb Garden Germination"
• Mark Hamill: "The Bow Tie Asymmetry"
• Stephen Hawking: "The Hawking Excitation", "The Extract Obliteration", "The Relationship Diremption", "The Troll Manifestation", "The Celebration Experimentation", "The Geology Elevation", "The Proposal Proposal"
• James Earl Jones: "The Convention Conundrum"
• Stan Lee: "The Excelsior Acquisition"
• Howie Mandel: "The Re-Entry Minimization"
• Joe Manganiello: "The D&D Vortex"
• Mike Massimino: "The Friendship Contraction", "The Countdown Reflection", "The Decoupling Fluctuation", "The Re-Entry Minimization", "The Table Polarization", "The First Pitch Insufficiency"
• Elon Musk: "The Platonic Permutation"
• Adam Nimoy: "The Spock Resonance"
• Bill Nye: "The Proton Displacement", "The Conjugal Configuration"
• Samantha Potter: "The Panty Piñata Polarization"[lower-alpha 9]
• Katee Sackhoff: "The Vengeance Formulation", "The Hot Troll Deviation" (both appearances are in a daydream scene)
• William Shatner: "The D&D Vortex"
• Charlie Sheen: "The Griffin Equivalency"
• Kevin Smith: "The Fortification Implementation", "The D&D Vortex"
• George Smoot: "The Terminator Decoupling"
• Brent Spiner: "The Russian Rocket Reaction"
• George Takei: "The Hot Troll Deviation" (appears in a daydream scene)
• Kip Thorne: "The Laureate Accumulation"
• Analeigh Tipton: "The Panty Piñata Polarization"[lower-alpha 10]
• Neil deGrasse Tyson: "The Apology Insufficiency", "The Conjugal Configuration"
• Adam West:[42] "The Celebration Experimentation"
• Wil Wheaton: See the Wil Wheaton section of this article.
• Steve Wozniak: "The Cruciferous Vegetable Amplification"

• Cyndi Lauper: "A Baby Tooth and the Egyptian God of Knowledge" (voice only, saying the words of the title of her song, "girls just want to have fun")
• Elon Musk: "A Patch, a Modem, and a Zantac®" in a flashforward scene set 27 years into the future.