Siryn

While Sean Cassidy was working on a deep undercover mission for Interpol, his wife Maeve gave birth to their daughter, Theresa, at Cassidy Keep, County Mayo, Ireland. Not much later, Maeve dies in an IRA bombing. With no means to contact Sean, his cousin Tom takes care of Theresa. When Sean returns to learn of his wife's death, he is devastated. Before Tom can even tell him of the existence of his daughter, Sean lashes out at Tom with his sonic scream for not having taken better care of Maeve. While Sean flies away in anger, Tom falls into a chasm, breaking his leg as a result of the attack, which leaves him with a limp. Tom swears to make Sean pay and vows to never tell him about his daughter, raising her himself instead.[2]

Tom (now known as Black Tom) trains Theresa as his apprentice in his criminal activities. While still a young teen, Theresa accompanies Black Tom and his then-partner, the Juggernaut, to San Francisco. Here, employing the name Siryn, she aids them in a theft of vibranium, and battles the original Spider-Woman.[3] Due to her inexperience, she performs poorly in battle and is defeated by Spider-Woman again during Black Tom's temporary capture. Initially believing her to be seriously hurt, Black Tom resolves to break all association with her so that she will not be exposed to further danger. While in custody, he exonerates Theresa of responsibility for her crimes,[4] and writes a letter to Sean explaining who she is. The X-Men bring Theresa back to their headquarters, where she is joyfully reunited with her father.[5]

X-Force #90 in which Feral injures Siryn.

Theresa soon moved to Muir Island, home of the research laboratories of Dr. Moira MacTaggert, a longtime ally of Professor Xavier. During an overnight visit to Xavier Institute, Siryn, Kitty Pryde, Illyana Rasputin, and a young Muir Island resident named Amp battled robotic duplicates of the Brotherhood of Evil Mutants after accidentally releasing them from the Danger Room. Later in the evening, Siryn engaged Kitty in a vicious fist fight after Amp convinced her that the young X-Man was trying to sabotage her chances with a young man named Dimitri. After the fight was broken up by Wolverine, the girls reconciled and left on friendly terms.[6] She also accompanied Wolverine and Kitty when they were asked by Professor Xavier to act as bodyguards for the mutant pop-star Dazzler. Dazzler was so impressed with Theresa's rendition of "Amazing Grace", that she asked the young mutant to act as a backing vocalist for her concert.[7]

While living back on the island, Siryn started a romantic relationship with the mutant known as Jamie Madrox. This version of Multiple Man turned out to be one of his many duplicates and not the original Multiple Man, leading to the end of the relationship. During this time Siryn and Multiple Man traveled to New York City.[8] She and Madrox began a search to help the New Mutants find two of their members, Sunspot and Warlock, who had run away from the school.[9] In the course of this adventure, Siryn and Multiple Man found Sunspot and met the association of street-level mutants known as the Fallen Angels.[10] They were transported, with the Fallen Angels, to Devil Dinosaur's planet.[11] They then traveled to the "Coconut Grove", the home planet of the alien Ariel.[12] While there, her superhuman powers were neutralized, and she was made a captive by Unipar of the "Coconut Grove" planet.[13] She regained her superhuman powers and freedom, and returned to Earth. She decided to remain in the Fallen Angels for a time to help reform their criminal members.[14]

Later, back on Muir Island, she fell under the mental control of the Shadow King.[15] Before long, she was freed from the Shadow King's control.[16]

Deadpool and Siryn, by Karl Kerschl

Siryn becomes a core member of X-Force, a paramilitary superhero team and for a time was its field leader. As a member of X-Force, her teammate Warpath develops a romantic interest in her while Siryn begins an ongoing flirtation with the mercenary Deadpool. Deadpool and Siryn initially became involved when the two met while fighting Black Tom Cassidy and the Juggernaut. Though Banshee warns Siryn that Deadpool was a madman and a murderer, she found herself quite taken with him, even looking past his horrific appearance. Due to this kindness, Deadpool becomes infatuated with Siryn and often sat outside her window as she slept in the X-Mansion. At first Siryn is unaware of this, but she is comforted in knowing that he is watching over her. Over time, Siryn became the voice of reason and sanity in Deadpool's ear, attempting to sway him to the side of good. She assists him in some of his missions, such as when Deadpool felt he needed some blood from the Hulk in order to cure problems with his own healing powers.[17] In the end Siryn becomes overwhelmed with balancing her duties with X-Force and the demands of Deadpool's somewhat faulty sanity. She promises him that she would consider progressing their relationship if he continues on the path of good, and once she has her X-Force responsibilities secured. Warpath continues to seek Siryn's affections, and makes his dislike for Deadpool clear during a visit to the baseball diamond used in the movie, Field of Dreams.[18]

Siryn confronts varied adversaries during her time in X-Force. She helps put down a coup in the other dimensional realm of Asgard. She confronts the forces of Onslaught and the interdimensional media mogul known as Mojo. She even battles S.H.I.E.L.D. forces on more than one occasion. She also confronts more down to earth problems, particularly alcoholism. Warpath helps her to cope with her drinking problems, and as of recent issues of X-Factor she is leading a sober lifestyle.

She becomes a vital part of the team, as opined by an aspect of Charles Xavier,[19] which saves the entire team from a near-death experience.

She leaves when Feral, a former teammate turned villain, slashes her throat, destroying her vocal cords and rendering her temporarily mute and powerless.[20]

Thanks to the aid of Deadpool, Siryn has since fully healed from her vocal cord injuries. Deadpool tracked down Wolverine and stole a sample of his blood to heal her.[21]

Siryn joins the Paris branch of the international mutant task force X-Corporation, claiming to atone for her father's sins for his failed X-Corps idea. There she reunites with old friends such as Multiple Man, Rictor and Cannonball, and works for the first time with Monet St. Croix.[22] Their first mission does not go well and Siryn has to deal with the loss of teammate Darkstar.[23]

Siryn leaves X-Corporation to become a member of X-Factor Investigations. As part of her initial duties for X-Factor Investigations, Siryn investigates the murder of a woman who died in a movie star's penthouse, on behalf of the victim's sister. A rival firm, Singularity Investigations, represented the actor with Damian Tryp, Jr. as the defense counsel and to prove the star innocent. Siryn and X-Factor Investigations manages to incriminate the star, and to thwart Singularity Investigation's assassination attempt on Rictor.[24] Damian Tryp Jr. is so infuriated that he later ambushes Siryn and beats her, leaving her to die in an alley. She was later found and taken hostage by a mentally ill former mutant only to be rescued by Rictor.[25]

While recovering from her injuries, Cyclops approaches Theresa and informs her Banshee has died. Upon hearing of his death, she goes into a state of denial, holding to the fact that many X-Men have been believed dead only to later return alive.[26]

During the Superhuman Civil War, Theresa opposes the registration act and is tasked with contacting more high-profile superheroes about the Decimation. After speaking with Spider-Man, X-Factor gets into contact with Quicksilver and Cyclops' team of X-Men demanding they answer why the reason behind the Decimation was kept secret and defy the registration act.[27]

Due to a love triangle with teammates Multiple Man and Monet St. Croix, Siryn's relationships become strained with both teammates. After spending a night drinking, Jamie Madrox awakens to learn that he and one of his duplicates slept with Theresa and Monet.[28] Although he is initially uncertain as to which was which,[29] he comes to conclude with near certainty that it was he that slept with Theresa, and the dupe that slept with Monet, though this does little to assuage Theresa and Monet's anger.[30] Theresa resolves her differences with both Madrox and Monet, and the two women develop a budding friendship after a shopping trip to Paris and partner together on later missions.[31]

Theresa and Monet are sent to retrieve two famous child singers (who specialize in mutant hate songs) from their parents, thanks to a court order from their grandparents. The two end up being ambushed, knocked out, and kidnapped by the children's mutant bodyguards, Solo and Clay. They awake imprisoned, (Theresa is tied up with her mouth covered by duct tape to prevent her from using her powers),[32] but they both escape and return the children to their grandparents. It is revealed that the entire mission was a ruse by Josef Huber to lure the women away from their X-Factor teammates. Both Monet and Siryn's mental-based powers negatively affect Huber's mind-control abilities.[33]

Theresa assists Rictor's infiltration of the Purifiers, and accompanies M and Strong Guy, along with the rest of the X-Men, to rescue the mutant baby and X-Force. She later receives a call from the mutant Peepers, who is being pursued by Predator X, but Theresa arrives too late to help him and finds what is left of his corpse.[34] Siryn prays at the comatose Jamie's bedside when he awakes, and takes part in the X-Men's assault on the Marauders' base with Monet and Guido, taking on Exodus in the battle.[35]

Theresa reveals that she is pregnant with Jamie's child, and after talking with Monet she reveals she intends on keeping it. When she attempts to tell Jamie he mistakenly believes that she wants to quit X-Factor. Monet later helps Theresa realize that she still loves Jamie and attempts to tell Jamie again but Arcade makes his presence known in Mutant Town; which he later destroys. After the ordeal is over, Jamie reveals he knows she is pregnant and the team moves to Detroit, Michigan to get away from Val Cooper and O*N*E.[36]

After the move to Detroit, Theresa becomes inactive during X-Factor's field missions. She comes to blows with Val Cooper upon finding out X-Factor has been under the employ of O*N*E since the destruction of Mutant Town. Val reveals her interest in Theresa's child and during a heated discussion, Theresa's water breaks and she is taken to a hospital.[37] As Theresa goes into labor, she proposes to Jamie who accepts. She gives birth to a boy, and they name him Sean after her father, whose death she finally accepts. Just hours after his birth, baby Sean is absorbed into Jamie's body as Jamie holds him, completely against Jamie's will, to the horror of Jamie, Theresa and the rest of X-Factor. Theresa attempts to save the baby and claws at Jamie's chest to get him back but pops some of her stitches and goes back into surgery. Later, Jamie reveals Sean was an "infant dupe", and was absorbed into him as a duplicate would, but a grieving Theresa, filled only with rage, declares after breaking Jamie's fingers that she will break his neck next time she sees him.[38]

After the pregnancy, Madrox leaves the team and Theresa takes charge, though she sinks into a depression because of recent events.[39] Following Madrox's return to the present, he offers to leave the team headquarters in Detroit and restart a branch with Guido in New York. She disbands the Detroit team, with the remaining members defecting to the New York branch. Theresa returns home to Ireland where she runs into Reverend John Maddox, one of Jamie's dupes. Reverend Maddox helps Theresa cope with depression and she has a one-night stand with Deadpool. After finally coming to terms with Banshee's death and reconciling her grief, Theresa retired the codename Siryn and takes her deceased father's codename as her own and begins calling herself Banshee in honor of his memory.[40]

After Cable and Hope Summers return to the present during X-Men: Second Coming, agents of the Mutant Response Division prepare to target Theresa for assassination when she attempts to return to America.[41] She is later rescued by Layla Miller and Shatterstar; together they teleport back to America and rejoin X-Factor in the final battle with the Mutant Response Division.[42]

Following the ordeal, Madrox accepts a new assignment from a disguised Hela who is searching for a missing pendant of Thor's hammer. When Jamie and Theresa track it down and take it off of the neck of a drunken bar patron, he reveals he is none other than Pip the Troll.[43] After a brief fight; Hela appears, captures Pip and teleports back to her base in Las Vegas.[44] Angered by this and feeling responsible, the team travel to Las Vegas and with the help of Thor, retrieve Pip from Hela's domain.[45]

The team is later hired by J. Jonah Jameson when an old friend of his is killed. Thinking the murderer may come after him, Theresa acts as his personal bodyguard. During a protest, Theresa receives an image of the murderer, who is revealed to be a woman named Ballistique. At that moment, Theresa sees Ballistique talking to J. Jonah Jameson and tries to attack by launching a powerful sonic scream at her but due to Ballistique's close proximity to Jameson, the police think Theresa is attempting to attack Jameson. The police attempt to stop Theresa by attacking her with their nightsticks but not before she can warn Monet of Ballistique.[46] During the ordeal, Guido is seriously wounded. Monet takes him to the hospital where Theresa attempts to console her.[47]

Theresa and the rest of X-Factor later become the target of various mystical Canine and Feline deities who are attempting capture Wolfsbane and her unborn baby. After the baby is born, it attempts to attack Theresa and Madrox but not knowing it is Rahnes son, Theresa uses one of her screams to blast it away from the duo.[48] Later while tracking a demon by the name of Bloodbath, Theresa is present when the demon kills Madrox.[49] After it is revealed Layla can bring back the dead, minus their soul, Theresa has no problems in asking Layla to return Madrox, putting her at odds with Monet for a while.[50]

After Havok and Polaris rejoin X-Factor, Theresa is present when Layla reveals Jamie has come back from the dead but not by her doing.[51] After returning from one of X-Factors missions, Theresa and Polaris share concern for Wolfsbane's wellbeing as she barely comes out of her room unless it's for missions. The two women decide to take Rahne on a road trip to Reverend John Maddox to help her. During the trip, Theresa and Lorna bond and develop a friendship.[52]

Wolverine later learns of a woman matching Theresa's description has been attacking and killing people in Ulster County, New York. Pairing up with Havok, the two investigate the murders.[53] Upon questioning the family of the murder victims, Theresa notices two photos featuring the families grandmother and granddaughter, both wearing Triquetras; a classic Celtic symbol associated with magic. She requests to speak with granddaughter as the grandmother was the first to die. At first believing the little girl to be a mutant, Theresa soon realizes the girl is not when she summons a Celtic goddess by the name of the Morrigan. The girl attempts to send the Morrigan back but she ignores the girl and takes Theresa; furious that she has been using the name Banshee, one of the many names associated with the Morrigan. Taking her to a lighthouse, the Morrigan offers Theresa a choice; apologize and worship her or die. Theresa rejects the Morrigans offer and is thrown to her death as her vocal cords had been weakened by the ordeal. Havok turns up just in time to see Theresa falling to her doom when she is rescued by a demon named Jezabel. Havok destroys the lighthouse leaving the Morrigan trapped under rubble. Jezebel advises them the apocalypse is coming and Theresa will have to make a tough choice sometime within the near future; to become part of a race of new gods or perish with the rest of humanity.[54]

Over the next few days, Theresa considers having an alcoholic beverage to help deal with what is going on when she is stopped by her father.[55] Unsure if he is real, she attempts to seek help from the other members of X-Factor only to find Polaris has lost her mind after the revelation she killed her parents and was manipulated by Magneto and Mastermind into not remembering, causing her to become mentally unbalanced throughout her life.[56] Theresa retreats back to her room where she continues to converse with Sean about the Morrigan and if he is real or some kind of hallucination when Layla enters, revealing she knows what is going on. Working with Layla, the duo attempt to summon the Morrigan but instead Theresa is teleported to Ireland. During the confrontation, Theresa asks if the Morrigan can heal Lorna but the Morrigan advises her she cannot as Lorna does not believe in her. The Morrigan reveals she is tired of being a goddess and misses her own father; if she wishes to truly help Lorna, she will need to become the Morrigan. Theresa agrees and then hurls a sonic lance through the Morrigan, killing her. In that moment, Lorna is completely healed of her insanity. Theresa teleports back to headquarters, appearing before Madrox as the Morrigan and telling him goodbye. Theresa lets him know she never stopped loving him and if he needs her, all he has to do is pray before departing.[56]

After Madrox is transformed into a demon, he takes her up on this offer so she rescues him from men in suits with weaponry and transforms him back into human form. She then asks the now-married Madrox and Layla if they want to reform the team but, they decline saying that (since Layla is pregnant) they have a farm to start up and a baby on the way.[57]

Theresa, back in her mortal form, is seen on Krakoa reunited with her father. During the celebration after the Quiet Council's first meeting, she uses her sonic powers in conjunction with Dazzler's light abilities to put on a light show for the people.[58]