Quote1.png My vocal cords are lethal. My estrogen level is berserk. Between Braxton-Hicks and my huge belly, I haven't slept in weeks. And I gotta pee... again. Free advice, Ms. Cooper. Never bet your life on what you think you know about a hormonal, sleep-deprived W.M.D. with a full bladder. Quote2.png
-- Siryn src



Theresa Maeve Rourke Cassidy is the mutant daughter of Sean, the mutant who was to become known as the Banshee, and Maeve Rourke Cassidy. Soon after his marriage, Sean Cassidy, an Interpol agent, was sent on an undercover anti-terrorist mission for many months, not knowing when he left that Maeve was pregnant. Shortly after Theresa's birth, Maeve took the infant Theresa with her on a visit to her relatives in Armagh in Northern Ireland. While she was there, Maeve, an innocent bystander, was killed in an IRA (Irish Republican Army) bombing along with a number of other people. No trace of Maeve was found by the authorities and they, and Maeve's relatives who knew of Theresa's existence, assumed that Theresa had also been killed in the explosion and never told Sean that Maeve had had a daughter.[10]

In fact, however, Black Tom Cassidy, her father's cousin and a rival for the love of her mother, had been present at the scene of the explosion and had secretly carried Theresa off with him. Black Tom suspected that Theresa might develop superhuman mutant powers as she grew older, and therefore he intended to raise her secretly so that he might exploit her powers himself. Sean was so filled with anguish when he returned and learned of Maeve's death that he left his ancestral home of Cassidy Keep and threw himself into a series of highly dangerous missions, eventually leading to his resignation from Interpol and his later involvement with the mutant villain team Factor Three.[10]


Theresa's sonic powers emerged at puberty and, a few years later, Black Tom began coercing her aid in committing crimes, whom she called "uncle" out of respect. At one point during high school, Theresa developed a drinking problem. However, Theresa's heart was never in a life of crime and she pursued it because the man who raised her, Black Tom, ordered her to do so. Eventually, Theresa accompanied Black Tom and his partner the Juggernaut to San Francisco.[11]

There, employing the name Siryn, Theresa battled the original Spider-Woman and several of the X-Men. This conflict ended in Black Tom's temporary capture. While in custody, Black Tom gentlemanly exonerated Theresa of responsibility for his crimes and wrote to Sean explaining who she was. Theresa and Sean were joyfully united at Professor Charles Xavier's mansion. Theresa went to live with her father, who had since retired back at Cassidy Keep and, due to his new girlfriend Dr. Moira MacTaggart, divided their time between Cassidy Keep and Muir Island.[12]

Fallen Angels

Sometime afterward, Theresa lived for a while at the Muir Island Mutant Research Center, owned by Dr. MacTaggert. There Theresa met, and developed a romantic relationship with Jamie Madrox, the Multiple Man. After being informed that the New Mutant Sunspot had run away, Theresa and Madrox helped to track down the young mutant. Traveling to New York, Theresa and Jamie found Sunspot and Warlock, attempting to rob a church for food, and Gomi propositioned Bobby Da Costa to join the Fallen Angels. Vanisher appeared to further persuade the children and, while still considering, Chance and Ariel appeared and challenged Sunspot to take a chance. Then Bobby, Warlock, and the duplicate Madroxes left with the group.[13]

After tracking the youths, Theresa and the original Madrox met Boom-Boom and were teleported to the Valley of the Flame, on Dinosaur World, where they were joined by Moon Boy and Devil Dinosaur. After Devil Dinosaur, accidentally, crushed Don the Lobster, Gomi's words of not leaving friends after an accident or tragedy struck a cord and Bobby began to second-guess his decision. After all of the mutant's powers, temporarily, went out-of-whack due to Chance, Ariel suggested that they all leave and teleported them to the Coconut Grove, her home planet. The inhabitants of the Coconut Grove and the leader, Unipar, captured the Fallen Angels, intending to use them as experiments to continue their evolution, but the Angels worked together to defeat them and return home. Sunspot and Warlock decided to return to the New Mutants, but Siryn and Madrox chose to remain with the Angels instead of going home to Muir Island.[14]

Muir Island

Siryn eventually returned to Muir Island, only to get caught up in the Shadow King's telepathic influence.[15] When the X-Men came to Muir to investigate, Siryn ended up fighting her own father Banshee, and took advantage of his feelings to beat him for the Shadow King.[16] She was freed from Farouk's influence with the other residents after the Shadow King was defeated on the physical and astral planes.[17]


Later, Theresa learned of an attempt by Black Tom and the Juggernaut to bomb the World Trade Center in New York, and she joined the formative group of mutants known as X-Force in defeating them.[13] She remained alongside the team for a long tenure, and eventually grew to become Field Leader during the absence of their former leader, Cable. On a solo adventure, Theresa encountered the mercenary Deadpool when both were tracking down activities of Black Tom. The two developed romantic feelings toward one another, but parted company.[13]

During her time with X-Force, Theresa's teammate Warpath developed a crush on her, and later he helped Theresa recover from a relapse into alcoholism.[10]

During a clash between X-Force and the villainous New Hellions, Theresa's vocal cords were severely damaged, causing her to lose her voice as well as her powers. Taking a leave of absence from the team, Theresa adjusted slowly to life without her powers, visiting with an aunt. Soon, however, Theresa walked into an antique store where the owner put a necklace on her. Theresa immediately began to talk again and flew off, the obvious victim of a possession, similar to the type performed by the deceased villain Malice.[18]

Later, Theresa encountered Deadpool who managed to get her to an organization that was able to heal her using the mutant healing power of their captive, the X-Men's Wolverine. Wolverine was upset at Deadpool, even after Theresa broke out of her healing tank, but Terry stood by Wade and flew off with him. What became of her possessor is unknown.[19]

X-Corps & X-Corporation

Banshee founded a mutant team, the X-Corps, as a paramilitary force that could police the mutant community. The team recruited several known villains and soon they embarked on a rampage through Paris until the X-Men were able to defeat them. Even so, Banshee was left wounded and the X-Corps was disbanded. Feeling the need to help atone for her father's debacle, Theresa offered her services to the X-Corporation, a clandestine extension of the X-Men operating as mutant champions on a worldwide scale.[20]

X-Factor Investigations

Siryn became a member of X-Factor Investigations. She was in a state of denial regarding her father's recent demise, correctly noting that many X-Men had been believed dead only to later return alive. Due to these recent traumas, Siryn was under considerable emotional strain.[21]

She was beaten by Damian Tryp, Jr. and captured by Doctor Leery. Rictor rescued her, killing Leery in the process.

During the Superhuman Civil War, Theresa opposed the Registration Act and was tasked with contacting more high-profile superheroes about the Decimation. After speaking with Spider-Man, X-Factor got 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.[22]

One night, Madrox got drunk; Jamie Prime and a dupe he described as his libido incarnate slept with Siryn and Monet. Jamie was not sure which of them slept with the dupe. Regardless, Jamie kept it going with the both of them, afraid of revealing that he was double-timing them. After a confrontation with Singularity Investigations the members of X-Factor met with Doc Samson, who encouraged Jamie to confess the truth to Monet and Siryn. They did not take it well.[23]

Baby Sean

Theresa discovered that she was pregnant with Madrox's child. After Mutant Town was destroyed by Arcade, X-Factor moved to Detroit. As Theresa went into labor, she proposed to Jamie who accepted. Eventually, she gave birth to a baby boy that she named Sean. Upon picking up Sean, Madrox absorbed him: he had been a dupe all along. Filled only with rage, Theresa declared after breaking Jamie's fingers that she would break his neck next time she saw him.[24]


After disbanding the Detroit branch of X-Factor Theresa went back to Ireland where she ran into Reverend John Maddox, one of Jamie's dupes. Reverend Maddox helped Theresa cope with depression and she had 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 took her deceased father's codename as her own and began calling herself Banshee in honor of his memory.[2]

The Morrigan

As Polaris continued to mentally deteriorate, Terry asked Layla Miller to help her contact the Morrigan in an attempt to save Lorna's sanity. The Morrigan revealed that her name was actually a title that was passed down from one woman to another and that she was tired of being the Morrigan. She would help Terry by giving her the power that was needed to heal Lorna's mind. To do this, Terry had to kill the Morrigan and become the new Morrigan. Theresa accepted and killed the Morrigan using a "Banshee's scream" in the form of a sonic lance, by the Morrigan's request. With her new godly powers, Terry easily saved Lorna.[25]

After Terry donned the title, she immediately left the team, only reappearing when Jamie Madrox prayed to her while he was stuck in his demonic form because of Mephisto and the events of the contest to kill Tier Sinclair. She was initially surprised at the context of her summoning because she didn't expect this to be when Jamie summons her. She then healed Jamie and defeated the policemen that attempted to arrest Layla. She filled Layla and Jamie in on their friends' lives, and later offered to rally the team herself but didn't because she learned that Layla and Jamie just wanted to raise their child in peace.[26]

House of X

Theresa, assuming a mortal form instead of that of the Morrigan, shared a knowing look with her recently resurrected father Banshee at the celebration following the first meeting of the Quiet Council. Using her sonic scream, she worked in concert with Dazzler to produce a lightshow for the the people of the burgeoning nation-state upon Krakoa.[27][28]



Banshee is a second generation mutant and possesses sonic acoustic powers similar to those of her father:

Acoustikinesis: The ability to create various sonic effects through the combined action of her vocal cords and limited psionic powers which can only be used in conjunction with the sounds she produces.

  • Sonic Scream: Siryn can cause her vocal cords to vibrate over a wide range of sonic frequencies and produce a volume of sound ranging up to at least 140 decibels. Siryn has thus the ability to shatter solid objects with a sonic scream. This ability is most likely augmented with her ability to wield mythological Banshee cries which were demonstrated as being louder than her own sonic scream.
  • Flight: Siryn can use the sonic vibrations of her scream as a carrier wave.
  • Sonic Lance: By focusing her sonic vibrations while screaming into an intense beam. This is used as a sort of "battering ram" that can stun or even destroy most solid objects.
  • Sonar: She can use her sonic powers as a form of sonar. By sending out a precise, pure note and listening to the returning, altered wavefront of the note, she can evaluate her surroundings in total darkness with varying degrees of resolution.
  • Sonic Null Field: She can project a field of silence in a area making no sound reach outside the area or no sound outside the area in.
  • Sonic Amplification: She can amplify sound carrier waves allowing her to hear conversations or noises from far off.
  • Sonic Shield: She can tighten sound waves around herself or others near her, making a barrier against outside attack.
  • Vocal Disorientation: The ability to change someone’s balance, by affecting their equilibrium using her sonic scream.
  • Vocal Trance: The ability to subtly influence peoples subconscious mind by changing the tones and vibrations of her voice using sonics, the effects tend towards blatant hypnosis. At times she's been even capable of calming down an enraged Hulk (when his rage is not so intense).
  • Vocal Unconsciousness: The ability to affect the fluid in someone’s ear causing the person to go unconscious.
  • Siren's Song: The ability to influence human beings with a certain pitch of her voice, causing them to fall in love with her without regard to gender or sexual orientation.
  • Sound Immunity: Siryn's hearing and equilibrium are unaffected by the effects of her scream and similar abilities.
  • Superhuman Vocal Stamina: Her vocal cords are tremendously strong, so that she can produce sonic effects through screaming constantly for hours at a time without noticeably tiring or injuring her vocal apparatus. Siryn's vocal cords and the interiors of her throat and mouth are also superhumanly tough, so that the intense pressures and constrictions that she produces do not cause her any injury.

Godly Aspect: After killing the Morrigan, it is assumed that she gained all of her powers:

  • Immortality: The Morrigan is a god and therefore does not age.
  • Superhuman Durability: She was able to take a direct hit from a gun that was able to destroy Layla Miller's shield without feeling discomfort.[26]
  • Teleportation: When Theresa first gained her godly powers, she was able to blink out of existence and appear next to Jamie Madrox.
  • Prayer Locator: She was able to deduce exactly where Jamie was and teleport to him simply because he was praying to her.


  • Her vocal cords are susceptible to injury from excessive strain in using sonic powers. She has also survived major injuries to her throat at the cost of her sonic powers temporarily. Excessive vocal cord strain can also cause her to temporarily lose her powers.[7] This is most likely no longer an issue as her godly physiology is much more durable now.
  • A recovering alcoholic.[10]
  • Since Theresa can't drink alcohol, she pours water into wine bottles so that she can pretend it is wine. She also does this to test if God is on her side. She says if Jesus loves her that he'll turn the water into wine.[citation needed]

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