Kathryn Merteuil

In the film, Kathryn is wealthy, beautiful and popular, part of the Upper East Side's social elite. Portrayed as a manipulative mastermind who uses and destroys people for her own amusement, she is also depicted as being addicted to cocaine, which she hides in her rosary, and it is suggested that she suffers from bulimia. She hides her true nature behind the facade of a deeply religious model student, fooling everyone she knows, except for her equally narcissistic step-brother Sebastian Valmont (Ryan Phillippe) and ex-boyfriend Court Reynolds (Charlie O'Connell). Kathryn shows signs of sociopathic and narcissistic traits, treating the death of her supposedly "beloved" step-brother with cold disdain, and gleefully enjoying destroying his life, as well as those of the people she perceives as threats or inferior to her. She has a strong superiority complex, but the extent of her interest in Sebastian is left ambiguous. Kathryn is the archetypal "ice princess" whose opulent bedroom is a cold, dark lair decorated in royal blue and silver with crystal embellishments. When she's not wearing black, gray or other dark, muted colors, she occasionally wears icy blue.

In the film, she's first seen discussing her prep school with Mrs. Caldwell (Christine Baranski) and her daughter, Cecile (Selma Blair). Kathryn promises Mrs. Caldwell that she will look out for the sheltered and naive Cecile. However, she reveals to Sebastian that her real intention is to use Cecile to take revenge on Court, who had dumped her for Cecile. Kathryn asks Sebastian to seduce Cecile; yet he refuses as he is planning to seduce virgin Annette Hargrove (Reese Witherspoon), the daughter of their school's new headmaster. The two make a wager: Kathryn believes he cannot get Annette to bed, yet Sebastian believes he can. If Kathryn wins, she gets Sebastian's vintage Jaguar XK140; if Sebastian wins, Kathryn will have sex with him.

After numerous failed attempts of seducing Annette, Sebastian agrees to seduce Cecile. Cecile confesses to Kathryn that her music teacher, Ronald Clifford (Sean Patrick Thomas), is in love with her. Afterwards Kathryn tells Mrs. Caldwell about Ronald and Cecile's romance and Mrs. Caldwell intervenes in their relationship. Sebastian, in turn, calls Cecile to his house, ostensibly to give her a letter from Ronald. There, he blackmails Cecile and performs oral sex on her. The next day, Cecile confides in Kathryn, who advises her to learn from Sebastian so that she can please Ronald in bed.

After Sebastian sleeps with Annette, Kathryn offers herself to Sebastian as he has won the bet, but he refuses; he has fallen in love with Annette. Kathryn begins showing signs of possessiveness towards Sebastian, and it is suggested that she is truly in love with him, in her way.[2] The next day, Kathryn taunts him and threatens to ruin Annette's reputation, so Sebastian feigns indifference to Annette and breaks up with her. After Sebastian tells Kathryn that he has broken up with Annette and arranged for Cecile and Ronald to be together, Kathryn reveals that she has known all along that he was truly in love with Annette and manipulated him into giving her up. Kathryn knows that he came to make plans for them to have sex, rejects him. Once he leaves, Kathryn calls Ronald to tell him that Sebastian slept with Cecile and (falsely) inform him that Sebastian hit her. This false information leads to Ronald attacking Sebastian and engineers his death. Only when he watches Sebastian and Annette profess their love before his death, Ronald realizes that Kathryn lied to him. At Sebastian's funeral, Kathryn tries to maintain her reputation by trying to make an example of Sebastian. Her former friends and everyone else furiously reject her by leaving and humiliating her in the process. Kathryn's spotless reputation is ruined when Cecile distributes copies of Sebastian's private journal, made into a book by Annette, titled "Cruel Intentions", which details her manipulations. Her fall from grace doesn't end there, as Ronald had made a detailed written confession about her involvement and how she lied to him about Cecile no longer being a virgin in order for him to kill Sebastian. This is made worse when Headmaster Hargrove finds her rosary and discovers drugs hidden in them. It is implied that the disapproving headmaster will expel her from the school.[3]

The straight-to-video prequel to the original film tells the story of Kathryn's younger years. The film reveals that Kathryn was born to Tiffany Merteuil (Mimi Rogers), a well-respected New York socialite. However, the prequel features several inconsistencies in its relation to the first film, such as the backstory concerning Kathryn's mother and Kathryn's meanspirited behavior, due to the film's origins as a TV series rather than a prequel. Kathryn attends Manchester Prep, a prestigious co-educational private school on the outskirts of the city. As in the first film, she manipulates and controls everyone around her, even seducing her school's headmaster, and then blackmailing him into letting her do whatever she wants. After her new step-brother Sebastian Valmont (Robin Dunne) and his father move in, Kathryn becomes jealous as Sebastian bests her in both piano and vocabulary.

The next day, at a school assembly, Kathryn, who is the student body president, delivers a speech to her classmates, but is interrupted by uncontrollable hiccups coming from a student, who then begins to choke on the gum that she was chewing in a bid to stop her hiccups. She is saved by the quick action of another fellow student, who performs the Heimlich maneuver, allowing the student to expel the gum, which ends up flying into Kathryn's hair. Afterwards Kathryn calls a meeting of the secret society of student elites, deciding upon the fate of the new students. This leads them to Cherie (Keri Lynn Pratt), the student with the hiccups, as well as the discovery that Cherie's family is wealthier than Kathryn's; this, and the events of the assembly, cause Kathryn to seek a vendetta against Cherie.

The next night, Kathryn calls Cherie, asking if she would like to attend a school event with her. She takes Cherie to a popular nightclub, and tricks her into drinking several Long Island Ice Teas. After getting the attention of a male club goer, Kathryn tells Cherie he clearly likes her and that she should have sex with him. Yet her plan fails once Cherie throws up on the young man's feet. After Sebastian angers Kathryn, whose day is interrupted by not being able to contact her driver, She conducts a plan to make him similar to her, and begins thinking on how she can mold Sebastian into a heartless womanizer. She starts by interfering with Sebastian's attempts to woo his classmate Danielle (Sarah Thompson). Kathryn first tries to tempt him away from Danielle by luring him with identical twins, who confide to Sebastian that Danielle is the only virgin at Manchester and she plans not to have sex with anyone unless she is truly in love.

Kathryn continues her attempt to sabotage Cherie, but it backfires, as Kathryn's mother tells her to become best friends with Cherie, in an attempt to encourage Cherie's mother to donate a large amount of money to the school. Sebastian soon professes his love for Danielle, only to find that she does not reciprocate. It turns out that Danielle is actually secretly working alongside Kathryn and is helping fulfill her secret plan to dupe Sebastian. Defeated by Kathryn's manipulation, a heartbroken Sebastian states he will never fall in love again; afterwards, he makes an alliance with Kathryn to dominate and manipulate others. She then tells Sebastian he should start with Cherie.

While Kathryn herself does not appear in the third film in the franchise, the main character in this film - Kathryn's equally manipulative cousin Cassidy Merteuil (Kristina Anapau) - reveals that Kathryn is currently a patient in a methadone clinic.