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Quote1 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

Theresa Cassidy, also known as Siryn, is the daughter of mutant Sean Cassidy (Banshee), from whom she inherited her sonic-based powers. After her mother's death, she was raised in secret by her cousin Black Tom Cassidy, who concealed her true parentage for years. As her powers emerged, she reluctantly aided her uncle in criminal activities.[25][13] She clashed with superheroes like Spider-Woman and the X-Men.[26] However, her path changed when Black Tom exonerated her and revealed her true identity to Sean. Reunited with her father, she joined the X-Men, living between Cassidy Keep and Muir Island.[25]

During her tenure with the Fallen Angels,[18] Theresa formed a romantic bond with one the duplicates of Jamie Madrox, the Mutiple Man, unaware he wasn't the original. She later joined X-Force,[27] becoming Deputy Leader and engaging in conflicts against various adversaries, including Black Tom and the Juggernaut.[28] Theresa faced personal struggles, battling alcoholism and coping with the loss of her powers.[29] After a hiatus from X-Force, Theresa regained her abilities through unconventional means involving Deadpool[30] and Wolverine[31]. With her powers returned she joined the X-Corporation[32] and later X-Factor Investigations.[22] Theresa faced challenges within the team, including betrayal and personal relationships, eventually leading to her leadership role.[33]

Theresa's life took a tragic turn when she became pregnant with Madrox's child, whom she named Sean, only for him to be absorbed by Madrox upon the birth.[34] Wrestling with grief and identity, Theresa retired the Siryn mantle,[4] reconciling with her past and embracing her heritage by adopting the Banshee in honor of her father.[20] As a member of Krakoa, Theresa faced new trials, including battles against the Morrigan's influence and her own mysterious deaths.[35] Through resilience and support from allies, she overcame these obstacles, reclaiming her agency and continuing her legacy as a formidable mutant hero.[36]


Early Life[]

Theresa 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, an Interpol agent, was sent on an undercover mission for many months, not knowing that Maeve was pregnant when he left. Shortly after Theresa's birth, Maeve, an innocent bystander, was killed in an IRA (Irish Republican Army) bombing along with a number of other people. Sean's cousin, Tom Cassidy, got custody of the baby and raised her as his own, hiding the truth from Sean as well as Theresa for decades.[25][19][37]

When Sean returned and learned of Maeve's death, he blamed Tom for not keeping the woman they both loved safe, becoming so filled with anguish when 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.[19][37]


Theresa's sonic powers emerged at puberty and, a few years later, Black Tom began coercing her aid in committing crimes. 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.[37] Eventually, Theresa accompanied Black Tom and his partner the Juggernaut to San Francisco.[26]

Theresa Cassidy (Earth-616) and Sean Cassidy (Earth-616) from Uncanny X-Men Vol 1 148 0001

Meeting her father for the first time

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.[26] 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.[25]

Fallen Angels[]

Theresa lived for a while at the Muir Island Mutant Research Center, owned by Dr. MacTaggert.[18] There, Theresa met and developed a romantic relationship with Jamie Madrox, the Multiple Man, unaware she was actually getting involved with a dupe.[29] After being informed that the New Mutant Sunspot had run away, Theresa and Madrox helped to track him down. Traveling to New York, Theresa and Jamie found Sunspot and Warlock and met the young mutants group known as the Fallen Angels. Unable to convince them to come back home, Siryn and Multiple Man joined the Fallen Angels as well.[38]

Theresa Cassidy (Earth-616) from Fallen Angels Vol 1 2 001

With the Angels, they met Boom-Boom, visited the Valley of the Flame, on Dinosaur World, and traveled to Coconut Grove, the home planet of their teammate Ariel. The inhabitants of the Coconut Grove 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. In the end, Sunspot and Warlock decided to return to the New Mutants, but Siryn and Madrox chose to remain with the Angels for a while longer, instead of going home to Muir Island.[39]

Muir Island[]

Siryn eventually returned to Muir Island, only to get caught up in the Shadow King's telepathic influence.[40] When the X-Men came to investigate, Siryn ended up fighting her own father, Banshee, and took advantage of his feelings to beat him for the Shadow King.[12] She was freed from Farouk's influence with the other residents after the Shadow King was defeated on the physical and astral planes.[41]


Theresa Cassidy (Earth-616) from X-Force Vol 1 33 001

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.[42] She remained alongside the team for a long tenure, even becoming Deputy Leader after Cannonball's departure.[43] 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.[44]

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.[19]

Theresa Cassidy (Earth-616) from X-Force Vol 1 50 001

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.[45] Taking a leave of absence from the team, Theresa adjusted slowly to life without her powers, moving in with an aunt who lived in the US. 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 possession.[37][46]

After being freed through unknown ways,[13] Theresa was taken by Wade Wilson, Deadpool, to an organization that was able to restore her voice using the mutant healing power of their captive, the X-Men's Wolverine. He eventually broke free and lashed out on Deadpool for capturing him and giving him away. During their fight, Terry's healing tank was shattered and she emerged fully powered once more.[47]

Wade and Wolverine stopped fighting and explained what had happened to her. Hearing this, Theresa thanked Wade for everything he had gone through, but told him she didn't support his methods and that he shouldn't have betrayed a good man like Wolverine.[47]

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.[48] 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.[49]

X-Factor Investigations[]

Following M-Day, Siryn became a member of X-Factor Investigations. As part of her duties, she investigated the murder of the woman who died in Jack Vaughn's penthouse under suspicious circumstances. Jack Vaughn (a movie star) claimed that the woman had been killed by her sister, Gloria Santiago, who was upset about the relationship between the two. Rival agency Singularity Investigations represented Jack Vaughn, with Damien Tryp, Jr. as the defense counsel, while Siryn and X-Factor Investigations tried to help Gloria. After Monet St. Croix established a mental bond with Gloria to assess the truth, she managed to incriminate Vaughn, which made Tryp, Jr. so infuriated, he severely beat Siryn and left her for dead (having shot her in the neck with a dart that prevented her from using her powers). She was then captured by Doctor Leery, but, with the help of Rictor, she escaped, getting Leery killed in the process. After this, she entered 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.[50]

X-Factor Vol 3 1 Textless

After meeting Singularity Investigations' CEO, Tryp, Sr., Madrox started suspecting Singularity Investigations wasn't responsible for the decimation, as he'd previously thought, so he asked Siryn to find out more about it from the heroes who might have been involved (by using her modulated voice to make them more suggestible). She learned from Spider-Man, and later from Quiksilver, that the X-Men (who had denied any involvement) were, in fact, central to the ending of the House of M and the subsequent Decimation. After a confrontation, X-Factor took a public stance in defiance of the Superhuman Registration Act and the X-Men decided not to interfere with Quicksilver as long as he stayed in Mutant Town.[51]

When X-Factor decided to break into Singularity Investigations, Siryn and Rictor were in charge of clearing the surveillance room, while the others retrieved files on the new virus being developed by the organization. After Tryp, Junior and Tryp, Senior showed up, Siryn was once again shot in the neck with a power-dampening dart, but this time she was equipped a Kevlar collar that allowed her to strike back against her attackers. Before the confrontation could escalate, however, Jamie urged the team to retreat and deal with other pressing subjects. Unbeknownst to them, one of Madrox's dupes had been left behind and blew up the whole building, apparently killing Tryp, Junior and Tryp, Senior.[33]

Theresa Cassidy (Earth-616) from X-Factor Vol 3 32 001

One night, Madrox got drunk, and a dupe he described as his libido incarnate slept with Siryn and Monet, but, back then, Jamie didn't know if he had slept with one of the women or if the dupe had slept with the two. Regardless, Jamie kept it going with the both of them, afraid of revealing that he was double-timing them. After the 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.[52][53][54]

Despite initially being mad at Monet, the two realized their quarrel was illogical. Thus, they decided to go to Paris on a private jet and clear their minds together. After doing some shopping, they came across some anti-mutant riots. Later, finding themselves facing local authorities, they ended up fleeing the country in a hurry, bringing with them an ex-mutant named Nicole, who'd supposedly lost her parents in the riots.[55] This girl was later revealed to be an android and part of an intricate plan to get rid of mutants for good, but Layla Miller dealt with it.[56]

Shortly after returning from her trip with Monet, Theresa discovered that she was pregnant with Madrox's child.[57][58] After Mutant Town was destroyed by Arcade, Theresa and Jamie talked about their baby and their future together. The team also discussed what to do next and, in the end, they agreed to move their headquarters to Detroit, where Theresa spent most of her pregnancy.[21]

Siryn no more[]

Shortly before giving birth, Terry proposed to Jamie, who vehemently accepted, claiming he thought she'd never ask. With contractions becoming more frequent and Terry feeling more pain, she lost control and broke all the windows of the hospital, but Jamie never left her side, even in surgery. After a complicated delivery, she gave birth to a boy and finally acknowledged the death of her father. The baby was then named Sean, in his honor. As Jamie held his son for the first time, tragedy struck and he absorbed Sean, leaving Theresa in a deep state of sorrow.[34]

Theresa Cassidy (Earth-616) from X-Factor Vol 1 200 002

At her family's mausoleum

Jamie also didn't deal well with the situation well and left X-Factor Investigations.[54] In his absence, Terry became the leader of the team, despite not being in her best state of mind.[59] After some time, she disbanded X-Factor and returned to her family's home in Ireland with Monet, who was hoping her friend would "recapture her soul".[4]

Still, Monet felt she wasn't getting better and left, hoping to find a solution. During her time alone, Terry ran into Reverend John Maddox, one of Jamie's dupes. After getting punched in the face by Terry, who thought he was the real Madrox making fun of her faith, Reverend Maddox actually helped Theresa cope with depression and find her peace with God. After finally coming to terms with Banshee's death and reconciling her grief, Theresa retired the codename Siryn and began calling herself Banshee in honor of her father.[4]

Shortly after this, she reconciled with Madrox and rejoined the team in New York.[20]

The Morrigan[]

When Madrox was dead for a short period of time, Havok (Alex Summers) and Polaris (Lorna Dane) took the leadership of the team.[60]

As Polaris began to mentally deteriorate, Terry asked Layla 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.[5]

Theresa Cassidy (Earth-616) from X-Factor Vol 1 244 0001

After Terry donned the title, she immediately left the team, only reappearing when Jamie 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, but she then healed Jamie and defeated the policemen that were trying 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.[61]

House of X[]

Theresa, seemingly free of Morrigan's, joined the mutant state of Krakoa and reunited with her recently resurrected father at the celebration of Krakoa's recognition as a sovereign nation. She joined the island band[62] and, using her sonic scream, worked in concert with Dazzler to produce a light show for all the mutants commemorating their new-found liberty.[17]

Later, her father was hurt by Amneth's forces on a mission with Unus the untouchable and Summoner to the other side of the External Gate. Wanting revenge on those who hurt him, she decided to accompany another team through the gate to bring back Unus, who had been captured. As they were betrayed by Summoner, she blasted the first Horsemen of Apocalypse with her sonic scream, allowing her teammates to escape.[63]

All-New X-Factor[]

Afterwards, a new X-Factor was created due to the influx of missing mutants and unknown deaths The Five couldn't process for the resurrection protocols. She was one of the first mutants on their investigation list, after she let out a sonic scream as she fell to her death on a Krakoan cliff.[14]

Theresa Cassidy (Earth-616) from X-Factor Vol 4 4 001

Back in her old suit

Resurrected by the Five, she died again 5 days later “[s]omewhere in the UK.” Upon another resurrection, X-Factor interrogated her about her mysterious deaths, but she avoided their questions and blatantly lied to them. When Theresa left the Boneyard, she was confronted by Lorna on why she wasn't being honest, prompting her to use her powers to bewitch Lorna into sabotaging the investigation on her.[6] It was later revealed Theresa was secretly still under the control of the goddess Morrigan and had made a deal with her to die a thousand times, instead of allowing the Morrigan to perform a ritual mass sacrifice on Krakoa.[3]

Noticing she was being "tailed" by Daken, she lured him into the Alberta wilderness, in the middle of a snowstorm, to kill him without having his teammates alerted, unaware he had a healing factor. He remained a few days out in the cold, impaled with a broken crossbeam, but was eventually rescued by Northstar, who had been told of Siryn's last whereabouts by Polaris after Rachel had telepathically removed the Morrigan's influence from her mind. By then, Theresa was nowhere to be found.[62]

X-Factor would eventually confront the Morrigan after her attack on their HQ, which resulted in most of the team's demise. Eye-Boy and Prodigy, who were the sole survivors, got all their teammates resurrected and, together, they planned a counter-attack that successfully inhibited Morrigan's influence on Theresa.[64]

After going through Terry's memories, they discovered the key to defeating the goddess was Terry's former X-Factor teammate Shatterstar, whose power could kill the Morrigan and free Theresa from the curse. Therefore, after a complex rescue operation, Shatterstar was brought to the island and performed his duty against the goddess, freeing Theresa once and for all.[3]

She later attended the second Hellfire Gala, where Micromax flirted with her. Terry later aided in the battle against the Typhon Group who wanted to create an international incident by poisoning Gorgon and a few other mutants. [36]

From the Ashes[]

After the X-Men's war with the terrorist organization Orchis, Siryn would be one of several mutants incarcerated in Graymalkin Prison.[65]


Power Grid[70]
:Category:Power Grid/Fighting Skills/Some Training:Category:Power Grid/Energy Projection/Single Type: Long Range:Category:Power Grid/Durability/Normal:Category:Power Grid/Speed/Speed of Sound:Category:Power Grid/Strength/Normal:Category:Power Grid/Intelligence/Normal


X-Factor Vol 3 5 Textless


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, reflexive psionic powers.[13]

  • 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.[66]
  • Flight: Siryn can use the sonic vibrations of her scream to fly at the speed of sound.[13]
  • Sonic Lance: By focusing her sonic vibrations while screaming into an intense beam. This is used as a sort of "battering ram" with great concussive force that can liquify and disintegrate targets.[66][13]
  • 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.[66]
  • Sonic Shield: She generates a psionic field that protects her from the detrimental effects of her powers. However, she can still be injured if pushed beyond certain limits.[13]
  • Vocal Disorientation: The ability to change someone’s balance, by affecting their equilibrium using her sonic scream.[13]
  • Vocal Trance: The ability to subtly influence people's subconscious mind by changing the tones and vibrations of her voice using sonics, the effects tend towards blatant hypnosis.[67][13]
  • Vocal Unconsciousness: The ability to affect the fluid in someone’s ear causing the person to go unconscious.[13]
  • Selective Hearing: Siryn can focus on or completely block any given sound in her environment. This not only allows her to be unaffected by her own powers, but also to be extremely good in surveillance situations.[13]
  • 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.[66]
Godly Aspect: After killing the Morrigan, it is assumed that she gained all of her powers.[5][62]




  • 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.[37]

Additional Attributes

  • A recovering alcoholic.[19]


  • Theresa is catholic.[4]
  • Theresa wears glasses when using the computer.[68]


  • Theresa used to pour water into wine bottles so that she could pretend it was wine. She also did it to test if God was on her side. She stated that if He loved her, then He'd turn the water into wine.[59]

See Also

Links and References


  1. X-Factor #239
  2. Spider-Woman #37
  3. 3.0 3.1 3.2 3.3 X-Factor (Vol. 4) #9
  4. 4.0 4.1 4.2 4.3 4.4 4.5 4.6 X-Factor #200
  5. 5.0 5.1 5.2 5.3 X-Factor #244
  6. 6.0 6.1 6.2 6.3 X-Factor (Vol. 4) #6
  7. Cable & Deadpool #18
  8. X-Factor #212
  9. X-Factor (Vol. 3) #11
  10. X-Factor (Vol. 3) #12
  11. X-Factor (Vol. 3) #3
  12. 12.0 12.1 Uncanny X-Men #278
  13. 13.00 13.01 13.02 13.03 13.04 13.05 13.06 13.07 13.08 13.09 13.10 Women of Marvel: Celebrating Seven Decades Handbook #1
  14. 14.0 14.1 X-Factor (Vol. 4) #5
  15. X-Men Unlimited Infinity Comic #26
  16. Wolverine: First Class #16
  17. 17.0 17.1 17.2 House of X #6
  18. 18.0 18.1 18.2 18.3 18.4 Fallen Angels #1
  19. 19.0 19.1 19.2 19.3 19.4 19.5 X-Force #31
  20. 20.0 20.1 20.2 X-Factor #206
  21. 21.0 21.1 X-Factor (Vol. 3) #32
  22. 22.0 22.1 X-Factor (Vol. 3) #1
  23. X-Force #5
  24. Fallen Angels #5
  25. 25.0 25.1 25.2 25.3 Uncanny X-Men #148
  26. 26.0 26.1 26.2 Spider-Woman #3738
  27. X-Force #3
  28. X-Force #9091
  29. 29.0 29.1 X-Force #17
  30. Deadpool (Vol. 2) #1
  31. Wolverine (Vol. 2) #154
  32. New X-Men #128
  33. 33.0 33.1 X-Factor (Vol. 3) #12
  34. 34.0 34.1 X-Factor (Vol. 3) #39
  35. X-Factor (Vol. 4) #79
  36. 36.0 36.1 X-Men Unlimited Infinity Comic #52
  37. 37.0 37.1 37.2 37.3 37.4 X-Force #91
  38. Fallen Angels #14
  39. Fallen Angels #48
  40. X-Men Annual #15
  41. Uncanny X-Men #280
  42. X-Force #34
  43. X-Force #47
  44. Deadpool (Vol. 2) #14
  45. X-Force #90
  46. X-Force #99100
  47. 47.0 47.1 Wolverine (Vol. 2) #154155
  48. Uncanny X-Men #401406
  49. New X-Men #128130
  50. X-Factor (Vol. 3) #17
  51. X-Factor (Vol. 3) #89
  52. X-Factor (Vol. 3) #10
  53. X-Factor (Vol. 3) #13
  54. 54.0 54.1 X-Factor (Vol. 3) #40
  55. X-Factor (Vol. 3) #1416
  56. X-Factor (Vol. 3) #2224
  57. X-Factor (Vol. 3) #21
  58. X-Factor (Vol. 3) #28
  59. 59.0 59.1 X-Factor (Vol. 3) #44
  60. X-Factor #230
  61. X-Factor #262
  62. 62.0 62.1 62.2 X-Factor (Vol. 4) #7
  63. X of Swords: Creation #1
  64. X-Factor (Vol. 4) #8
  65. Free Comic Book Day 2024: Blood Hunt/X-Men #1
  66. 66.0 66.1 66.2 66.3 Official Handbook of the Marvel Universe (Vol. 2) #12
  67. X-Factor (Vol. 3) #22
  68. Domino (Vol. 2) #3
  69. Women of Marvel: Celebrating Seven Decades Handbook #1
  70. X-Factor Vol 1 200