Siryn

Theresa Cassidy debuted as a villain in Spider-Woman #37 (April 1981), created by writer Chris Claremont and artist Steve Leialoha.{{cite book |last1=DeFalco |first1=Tom |title=The Marvel Encyclopedia |last2=Sanderson |first2=Peter |last3=Brevoort |first3=Tom |last4=Teitelbaum |first4=Michael |last5=Wallace |first5=Daniel |last6=Darling |first6=Andrew |last7=Forbeck |first7=Matt |last8=Cowsill |first8=Alan |last9=Bray |first9=Adam |date=2019 |publisher=DK Publishing |isbn=978-1-4654-7890-0 |page=335}} She later appeared in the 1987 Fallen Angels series.{{Cite web |last=Marnell |first=Blair |date=March 17, 2019 |title=A St. Patrick's Day Salute to Siryn |url=https://www.marvel.com/articles/comics/a-st-patrick-s-day-salute-to-siryn |access-date=May 20, 2023 |website=Marvel.com}}{{Cite web |last=Derman |first=Matt |date=August 14, 2014 |title=1987 And All That: Fallen Angels #1-8 |url=https://www.cbr.com/1987-and-all-that-fallen-angels-1-8/ |access-date=May 20, 2023 |website=Comic Book Resources |language=en}} She appeared in the 1991 X-Force series. She appeared in the 1994 Deadpool: Sins of the Past series.{{Cite web |last=Hill |first=Brad |date=May 29, 2022 |title=From 'Dead Presidents' to '5 Ronins': 9 best Deadpool comics that every fan should read |url=https://www.sportskeeda.com/comics/9-best-deadpool-comics-every-fan-read |access-date=May 20, 2023 |website=Sportskeeda |language=en-us}}{{Cite web |last=Jasper |first=Gavin |date=May 24, 2018 |title=Deadpool Reading Order: Get to Know The Merc With a Mouth |url=https://www.denofgeek.com/comics/deadpool-reading-order-get-to-know-the-merc-with-a-mouth/ |access-date=May 20, 2023 |website=Den of Geek |language=en-US}} She appeared in the 1997 Deadpool series.

Theresa Cassidy appeared in the 2005 Cable and Deadpool series. She later appeared in the 2006 X-Factor series. She appeared in the 2021 X-Factor series.{{Cite web |last=Terror |first=Jude |date=January 11, 2021 |title=In This Issue, a Character Will DIE! - X-Factor #6 [XH] |url=https://bleedingcool.com/comics/in-this-issue-a-character-will-die-x-factor-6-xh/ |access-date=May 20, 2023 |website=Bleeding Cool |language=en}}{{Cite web |author1=Arrant |first=Chris |date=May 6, 2021 |title=A dark side to X-Men Founders' party revealed in X-Factor #9 preview |url=https://www.gamesradar.com/a-dark-side-to-x-men-founders-party-revealed-in-x-factor-9-preview/ |access-date=May 20, 2023 |website=Newsarama |language=en}}

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. Maeve later dies in an IRA bombing, and with no means to contact Sean, his cousin Tom takes care of Theresa. When Sean returns and learns of his wife's death, he is devastated. Before Tom can tell him about Theresa, Sean lashes out at Tom with his sonic scream for not having taken better care of Maeve. As Sean flies away in anger, Tom falls into a chasm and breaks his leg, leaving him with a limp. Tom swears to make Sean pay and vows to never tell him about his daughter, and raises her himself.X-Force (vol. 1) #31 Marvel Comics.

Tom (now known as Black Tom) trains Theresa as his apprentice in his criminal activities. As a young teen, she accompanies him and his then-partner, the Juggernaut, to San Francisco. She takes the name Siryn, aids them in a vibranium theft, and battles the original Spider-Woman.Spider-Woman #37. Marvel Comics. 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 absolves Theresa of all responsibility for her crimes,Spider-Woman #38 Marvel Comics. 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.Claremont, Chris. Uncanny X-Men #148 Marvel Comics.

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Theresa moves to Muir Island, home of the research laboratories of Moira MacTaggert, a longtime ally of Professor Xavier.{{Volume needed|c=y|date=April 2009}} During an overnight visit to Xavier Institute, Siryn, Kitty Pryde, Illyana Rasputin, and a young Muir Island resident named Amp battle robotic duplicates of the Brotherhood of Evil Mutants after accidentally releasing them from the Danger Room. Later in the evening, Siryn gets into a fist fight with Kitty after Amp convinces her that Kitty was trying to sabotage her chances with a young man named Dimitri. After the fight is broken up by Wolverine, the girls reconcile and leave on friendly terms.Van Lente, Fred. Wolverine: First Class #6 Marvel Comics. She also accompanies Wolverine and Kitty when they are asked by Professor Xavier to act as bodyguards for the mutant pop-star Dazzler. Dazzler is impressed with Theresa's rendition of "Amazing Grace" and asks her to act as a backing vocalist for her concert.David, Peter (w). Wolverine: First Class #16. Marvel Comics.

On the island, Siryn starts a romantic relationship with Jamie Madrox.{{Volume needed|c=y|date=April 2009}} This version of Multiple Man is revealed to be one of his many duplicates and not the original Multiple Man, leading to the end of the relationship.{{Volume needed|c=y|date=April 2009}} During this time Siryn and Multiple Man travel to New York City.Fallen Angels #1 Marvel Comics. She and Madrox search for two members of the New Mutants: Sunspot and Warlock, who had run away from the school.Fallen Angels #2 Marvel Comics. Siryn and Multiple Man find Sunspot and meet the association of street-level mutants known as the Fallen Angels,Fallen Angels #3 Marvel Comics. and they are all transported to Devil Dinosaur's planet.Fallen Angels #4. Marvel Comics. They travel to the Coconut Grove, the home planet of the alien Ariel.Fallen Angels #6. Marvel Comics. While there, her superhuman powers are neutralized and she is made a captive by Unipar.Fallen Angels #7. Marvel Comics. She regains her superhuman powers and returns to Earth. She chooses to remain in the Fallen Angels for some time to help reform their criminal members.Fallen Angels #8. Marvel Comics.

Back on Muir Island, she briefly falls under the mental control of the Shadow King.Claremont, Chris. Uncanny X-Men #278 Marvel Comics.Claremont, Chris. Uncanny X-Men #280. Marvel Comics.

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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 she begins flirting with Deadpool. Deadpool and Siryn become involved when the two fight Black Tom Cassidy and the Juggernaut. Although Banshee warns Siryn that Deadpool is a madman and a murderer, she finds Deadpool attractive, and the feelings are reciprocated. Over time, Siryn becomes the voice of reason and sanity in Deadpool's ear. She assists him in some of his missions, such as when Deadpool felt he needed blood from the Hulk to cure problems with his own healing powers.Deadpool Vol. 3 #4 In the end Siryn becomes overwhelmed with balancing her duties with X-Force and the demands of Deadpool's mental health. 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 Field of Dreams.Deadpool (vol. 3) #12. Marvel Comics.

Siryn confronts various adversaries during her time in X-Force: she puts down a coup in Asgard, and confronts Onslaught, Mojo, and S.H.I.E.L.D. on more than one occasion. Warpath helps her cope with her drinking problems, eventually leading her to become sober.{{Volume needed|c=y|date=April 2010}}

She becomes a vital part of the team, as opined by an aspect of Charles Xavier,X-Force (vol. 1) #68. Marvel Comics. which saves the entire team from a near-death experience.{{Volume needed|c=y|date=April 2010}}

She leaves when Feral, a former teammate turned villain, slashes her throat, destroying her vocal cords and rendering her temporarily mute and powerless.X-Force (vol. 1) #90 (May 1999). Marvel Comics.

Deadpool tracks down Wolverine and steals a sample of his bloodWolverine #154 - #155 (Sept, Oct 2000), Marvel Comics. to heal Siryn, who regains the use of her vocal cords.{{Volume needed|c=y|date=January 2012}}

Siryn joins the Paris branch of X-Corporation, claiming to atone for her father's sins for his failed X-Corps idea, where she reunites with Multiple Man, Rictor and Cannonball. She works with Monet St. Croix for the first time.New X-Men (vol. 1) #128, Marvel Comics. Their first mission does not go well and Siryn deals with the loss of her teammate, Darkstar.New X-Men (vol. 1) #130 (Oct 2002), Marvel Comics.

Siryn leaves X-Corporation to become a member of X-Factor Investigations. As part of her initial duties for X-Factor Investigations, she 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, represents the actor with Damian Tryp as the defense counsel. Siryn and X-Factor Investigations manage to incriminate the star and thwart Singularity Investigation's assassination attempt on Rictor.David, Peter (w). X-Factor (vol. 3) #8-9 (March - April 2006). Marvel Comics. Tryp later ambushes Siryn and beats her, leaving her to die in an alley. She is later found and taken hostage by a mentally ill former mutant only to be rescued by Rictor.David, Peter (w). X-Factor (vol. 3) #5. Marvel Comics.

While recovering from her injuries, Cyclops approaches Theresa and informs her Banshee has died. She goes into a state of denial, holding on to how many X-Men have been believed dead have returned alive.David, Peter (w). X-Factor (vol. 3) 7. Marvel Comics.

During "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.David, Peter (w). X-Factor (vol. 3) #8-9. Marvel Comics.

Siryn's relationships with Multiple Man and Monet become strained. After spending a night drinking, Madrox awakens to learn that he and one of his duplicates slept with Theresa and Monet.David, Peter. X-Factor #10 Marvel Comics. (October 2006) Although he is initially uncertain as to which was which,David, Peter (w). X-Factor #13 (January 2007). Marvel Comics. he concludes with near certainty that he slept with Theresa, and the dupe slept with Monet, though this does little to assuage Theresa and Monet's anger.David, Peter (w). X-Factor #14 Marvel Comics. (February 2007) 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.David, Peter (w). X-Factor (vol. 3) #15. Marvel Comics.

Siryn and Monet are sent to retrieve two famous child singers (who specialize in mutant hate songs) from their parents. The two are ambushed, knocked out, and kidnapped by the children's mutant bodyguards, Solo and Clay. They awake imprisoned,David, Peter (w). X-Factor (vol. 3) #22. Marvel Comics. 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, as both Monet and Siryn's mental-based powers negatively affect Huber's mind-control abilities.David, Peter (w). X-Factor (vol. 3) #21-24. Marvel Comics.

Theresa assists Rictor's infiltration of the Purifiers{{Volume needed|c=y|date=September 2014}} and accompanies the X-Men to rescue the mutant baby and X-Force.{{Volume needed|c=y|date=September 2014}} She later receives a call from Peepers, who is being pursued by Predator X, but Theresa arrives too late to help him and finds his remains.David, Peter (w). X-Factor (vol. 2) #26 (2008). Marvel Comics. Siryn prays at Madrox's bedside when he awakes, and takes part in the X-Men's assault on the Marauders' base with Monet and Guido, fighting Exodus in the battle.David, Peter (w). X-Factor (vol. 2) #27 (2008). Marvel Comics.

Siryn reveals that she is pregnant with Jamie's child, and after talking with Monet reveals she intends to keep it. When she attempts to tell Jamie he mistakenly believes that she wants to quit X-Factor. Monet later helps Siryn realize that she still loves Jamie. Siryn tries to tell him again, but Arcade appears and destroys Mutant Town. Afterwards, Jamie reveals he knows she is pregnant and the team moves to Detroit, Michigan, to get away from Val Cooper and O*N*E.David, Peter (w). X-Factor (vol. 3) #28-32. Marvel Comics.

After moving to Detroit, Theresa becomes inactive during X-Factor's field missions. She gets into an argument with Val 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.David, Peter (w). X-Factor (vol. 3) #33-37. Marvel Comics. 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. Hours after his birth, baby Sean is absorbed into Jamie's body as Jamie holds him, to his horror. 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. Jamie reveals Sean was an "infant dupe", and was absorbed into him as a duplicate would, but Theresa declares that she would break his neck the next time she sees him after breaking his fingers.David, Peter (w). X-Factor (vol. 3) #39. Marvel Comics.

After the pregnancy, Jamie leaves the team and Theresa takes charge, though she sinks into a depression.David, Peter (w). X-Factor (vol. 3) #41. Marvel Comics. Following Jamie's return to the present, he offers to leave the team headquarters in Detroit and start 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, who helps her cope with depression. She later has a one-night stand with Deadpool. After coming to terms with Banshee's death and reconciling her grief, Theresa retires the codename Siryn and takes her deceased father's codename as her own, calling herself Banshee in honor of his memory.David, Peter (w). X-Factor (vol. 3) #200. Marvel Comics.

After Cable and Hope Summers return to the present during X-Men: Second Coming, agents of the Mutant Response Division target Theresa for assassination when she attempts to return to America.David, Peter (w). X-Factor (vol. 3) #204. Marvel Comics. She is rescued by Layla Miller and Shatterstar, and they teleport back to America and rejoin X-Factor in the final battle with the Mutant Response Division.David, Peter (w). X-Factor (vol. 3) #205-206

Afterwards, Jamie 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 Pip the Troll.David, Peter (w). X-Factor (vol. 3) #207. Marvel Comics. After a brief fight, Hela appears, captures Pip, and teleports back to her base in Las Vegas.David, Peter (w). X-Factor (vol. 3) #208 The team travel to Las Vegas and with the help of Thor, retrieve Pip from Hela's domain.David, Peter (w). X-Factor (vol. 3) #209-212. Marvel Comics.

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 about Ballistique.David, Peter (w). X-Factor (vol. 3) #217. Marvel Comics. During the ordeal, Guido is seriously wounded, and Monet takes him to the hospital where Theresa attempts to console her.David, Peter (w). X-Factor (vol. 3) #218. Marvel Comics.

Theresa and the rest of X-Factor later become the target of various mystical canine and feline deities who attempt to capture Wolfsbane and her unborn baby. After the baby is born, it attempts to attack Theresa and Jamie but not knowing it is Rahne's son, Theresa uses one of her screams to blast it away from the duo.David, Peter (w). X-Factor (vol. 3) #220-224 Later, while tracking a demon by the name of Bloodbath, Theresa witnesses it kill Jamie.David, Peter (w). X-Factor (vol. 3) #227 After it is revealed Layla can bring back the dead, minus their soul, Theresa has no problems in asking Layla to return Jamie, putting her at odds with Monet for a while.David, Peter (w). X-Factor (vol. 3) #228-230. Marvel Comics.

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.X-Factor Vol. 3 #234 After returning from one of X-Factor's missions, Theresa and Polaris share concern for Wolfsbane's wellbeing as she barely comes out of her room unless it is 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.X-Factor Vol. 3 #237. Marvel Comics.

Wolverine learns that 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.David, Peter (w). X-Factor (vol. 3) #238. Marvel Comics. Upon questioning the family of the murder victims, Theresa notices two photos featuring the family's grandmother and granddaughter, both wearing triquetras. Although she first believes the little girl to be a mutant, Theresa realizes the girl is not when she summons a Celtic goddess, 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. The Morrigan takes Theresa to a lighthouse and offers her a choice: apologize and worship her, or die. Theresa rejects the Morrigan's offer and is thrown to her death as her vocal cords had been weakened by the ordeal. Havok arrives 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.David, Peter (w). X-Factor (vol. 3) #239. Marvel Comics.

Over the next few days, Theresa considers drinking alcohol to help deal with what is going on when she is stopped by her father.David, Peter (w). X-Factor Vol. 3 #241. Marvel Comics. 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.David, Peter (w). 'X-Factor (vol. 3) #244. Marvel Comics. Theresa goes 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, who reveals she knows what is going on. Theresa and Layla attempt to summon the Morrigan but Theresa is teleported to Ireland instead. 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 Theresa wants to help Lorna, she must become the Morrigan. Theresa agrees and 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 Jamie 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.

After Jamie is transformed into a demon, he takes her up on this offer so she rescues 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 they have a farm to start up and a baby on the way.David, Peter (w). X-Factor (vol. 3) #262. Marvel Comics.

Theresa Cassidy, 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.Hickman, Jonathan (w). House of X #6. Marvel Comics.

Theresa Cassidy possesses the ability to emit high-decibel sonic screams to create various sonic effects with her vocal cords. She can vary the pitch to deflect projectiles. She possesses an enhanced sense of hearing and can use her voice to detect objects via echolocation.Official Handbook of the Marvel Universe Vol 2 #12 Siryn is able to fly at the speed of sound while screaming.Women of Marvel: Celebrating Seven Decades Handbook #1 She has potent sonic attacks that can shatter objects, project concussive blasts of sonic force (a "sonic lance"). and cause immediate pain, nausea and vomiting, and unconsciousness. She has shown a degree of resistance to sounds and vibrations that would be harmful or painful to normal humans and mutants without sonic-based powers.David, Peter. X-Factor (vol. 3) #30 Marvel Comics. Theresa Cassidy is able to influence and control other human beings with her sonic voice, and cause them to enter a hypnotic state.X-Factor Vol 3 #22 She can cause the intended person to fall in love with her without regard to gender or sexual orientation and carry out her wishes and commands, like mythical Sirens.David, Peter. X-Factor (vol. 3) #1. Marvel Comics. January 2006 Theresa Cassidy once used this ability on Spider-Man, forcing him to divulge the truth about the Decimation of the mutants.David, Peter. X-Factor (vol. 3) #8. Marvel Comics. August 2006 She can prevent others from hearing external sounds by a certain vocal pitch so that she can secretly deliver messages to them.Cable & Deadpool #17. Marvel Comics.

Theresa Cassidy gained numerous undefined mystical abilities when she killed the Morrigan. Her known powers include the ability to teleport by her own free will or to people who summon her using the correct ritual, heal her followers and people with a personal bond to her, and some form of immortality or longevity. She is able to revert Jamie to his human form and absorb laser blasts from a gun that can destroy Layla Miller's force field.David, Peter. X-Factor Vol. 3 #262. Marvel Comics.

Deirdre Kaye of Scary Mommy called Theresa Cassidy a "role model" and a "truly heroic" female character.{{Cite web |last=Kaye |first=Deidre |date=November 16, 2020 |title=Looking For A Role Model? These 195+ Marvel Female Characters Are Truly Heroic |url=https://www.scarymommy.com/marvel-female-characters |access-date=January 25, 2023 |website=Scary Mommy |language=en}} Dalton Norman of Screen Rant included Theresa Cassidy in their "10 Best Marvel Characters Who Made Their Debut In Spider-Man Comics" list.{{Cite web |last=Norman |first=Dalton |date=May 17, 2022 |title=The 10 Best Marvel Characters Who Made Their Debut In Spider-Man Comics |url=https://screenrant.com/marvel-comics-best-characters-debuts-spider-man-issues/ |access-date=January 26, 2023 |website=Screen Rant |language=en}} Darren Franich of Entertainment Weekly ranked Theresa Cassidy 34th in their "Let's Rank Every X-Man Ever" list.{{Cite magazine |last=Franich |first=Darren |date=May 21, 2014 |title=Let's rank every X-Man ever |url=https://ew.com/article/2014/05/21/x-men-best-worst/ |access-date=January 26, 2023 |magazine=Entertainment Weekly |language=en}} Comic Book Resources ranked Theresa Cassidy 7th in their "8 X-Men Kids Cooler Than Their Parents (And 7 Who Are Way Worse)" list,{{Cite web |last=Webber |first=Tim |date=April 9, 2018 |title=8 X-Men Kids Cooler Than Their Parents (And 7 Who Are Way Worse) |url=https://www.cbr.com/x-men-kids-cooler-than-parents/ |access-date=January 25, 2023 |website=Comic Book Resources |language=en}} 10th in their "20 Most Powerful Mutants From The '80s" list,{{Cite web |date=September 2, 2018 |title=Fast Times At Mutant High: The 20 Most Powerful Mutants From The '80s |url=https://www.cbr.com/powerful-mutants-80s/ |access-date=January 26, 2023 |website=Comic Book Resources |language=en}} and 15th in their "X-Force: 20 Powerful Members" list.{{Cite web |last=Wyse |first=Alex |date=April 11, 2018 |title=X-Force: 20 Powerful Members Ranked From Weakest To Strongest |url=https://www.cbr.com/x-force-members-ranked/ |access-date=January 25, 2023 |website=Comic Book Resources |language=en}}

An alternate version of Theresa Cassidy appears in the 1995–1996 "Age of Apocalypse" storyline. She is known as Sonique. She is a companion to Nate Grey, and fights alongside him and Sauron against Mr. Sinister.Jeph Loeb. X-Man #1 - 4 (March - June 1995) Marvel Comics She is temporarily a member of the Sinister Six, who aid Sinister in attacking the X-Men, after being brainwashed by Jean Grey. She is freed from Grey's influence by Psylocke.Akira Yoshida. "Chrysalis" X-Men: Age of Apocalypse #6 (June 2005) Marvel Comics

An alternate version of Theresa Cassidy appears in the Ultimate Universe. She is seen as one of William Stryker Jr.'s hostages before being rescued by Kitty Pryde and the new X-Men.Ultimate Comics: X-Men #5-6. Marvel Comics.

An alternate version of Theresa Cassidy appears in the story "What If the X-Men Died on their First Mission?." After the X-Men's death on Krakoa, Beast hastily assembles a mutant team to combat Count Nefaria and his Ani-Men. At this point, Theresa is still under the guardianship of Black Tom and unaware of her father's existence and death. After learning the facts from Beast, she names herself Banshee in her father's honor. After foiling Nefaria and settling her affairs with Black Tom, she joins the newly formed X-Men team.What If vol. 2 #9 (1990). Marvel Comics.

• Theresa Rourke / Siryn appears in X2, portrayed by Shauna Kain.{{Cite web |date=October 4, 2014 |title=X-Men Movies: The Complete Mutant Character Guide |url=https://screenrant.com/x-men-movies-characters-mutants/ |access-date=August 11, 2023 |website=ScreenRant |language=en}}{{Citation |last=Singer |first=Bryan |title=X2 |date=2003-05-02 |url=https://www.imdb.com/title/tt0290334/?ref_=nm_flmg_t_4_act |type=Action, Sci-Fi, Thriller |access-date=2023-08-11 |others=Patrick Stewart, Hugh Jackman, Halle Berry |publisher=Twentieth Century Fox, Marvel Enterprises, Donners' Company}} This version is a student of the Xavier Institute and roommate of Kitty Pryde.
• Theresa Rourke / Siryn makes a cameo appearance in X-Men: The Last Stand, portrayed again by Shauna Kain.{{Citation |last=Ratner |first=Brett |title=X-Men: The Last Stand |date=2006-05-26 |url=https://www.imdb.com/title/tt0376994/?ref_=nv_sr_srsg_0_tt_7_nm_1_q_x-men%2520the%2520last |type=Action, Adventure, Sci-Fi |access-date=2023-08-11 |others=Patrick Stewart, Hugh Jackman, Halle Berry |publisher=Twentieth Century Fox, Marvel Enterprises, Donners' Company}}

Theresa Cassidy / Siryn received an action figure in Hasbro's Marvel Legends line.{{Cite web |date=February 8, 2022 |title=Wolverine Faces Off Against More Villains in New Wave of Hasbro Marvel Legends Figures |url=https://www.laughingplace.com/w/news/2022/02/08/wolverine-villains-wave-two-hasbro-marvel-legends/ |access-date=May 20, 2023 |website=LaughingPlace.com |language=en-US}}{{Cite news |last=Dar |first=Taimur |date=February 8, 2022 |title=Maggott (plus Eany and Meany!) among latest Hasbro Marvel Legends X-Men toy reveals |url=https://www.comicsbeat.com/maggott-hasbro-x-men-marvel-legends-reveals/ |access-date=May 20, 2023 |website=Comics Beat |language=en-US}}

{{Reflist|30em}}

• [https://web.archive.org/web/20000823043806/http://www.redsresources.com/siryn/ The Woman Behind the Voice]
• [https://web.archive.org/web/20140625194803/http://uncannyxmen.net/characters/siryn UncannyXmen.net Spotlight On Siryn]

{{X-Men characters}}

{{X-Force}}

Category:Characters created by Chris Claremont

Category:Comics characters introduced in 1981

Category:Fictional characters who can manipulate sound

Category:Fictional superhuman healers

Category:Fictional hypnotists

Category:Fictional Irish people

Category:Fictional private investigators

Category:Irish superheroes

Category:Marvel Comics characters who can teleport

Category:Marvel Comics female superheroes

Category:Marvel Comics mutants

Category:Marvel Comics orphans

Category:X-Factor (comics)