Quote1.png Saints preserve me... l-l-lad, ye're a... mutant?! Quote2.png
-- Banshee src


Early Years

Sean Cassidy was born as the heir to the castle and estate of Cassidy Keep, Ireland, as well as a small fortune. After graduating from Trinity College, Dublin, with the degree of Bachelor of Science, Cassidy became a detective at Interpol, the international law enforcement organization. By the time he married Maeve Rourke, Cassidy had risen to the rank of Inspector at Interpol. Although Cassidy had discovered his mutant powers in his adolescence, he kept them secret, even from the rest of Interpol.[citation needed]

However, Cassidy's powers were known to his disreputable cousin, Black Tom Cassidy, who had discovered that he himself was a superhumanly powerful mutant. Sean and Black Tom had long been rivals, especially over the love of Maeve, before she ultimately married Sean.[citation needed]

Sean was assigned by Interpol to a top secret mission which required that he stay out of touch with his family for a considerable amount of time. When he left on the mission, Maeve was in her first month of pregnancy, although neither Sean nor Maeve knew it at the time. Their daughter, Theresa, was born during Sean's absence. 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. In fact, however, Black Tom Cassidy 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.[citation needed]

On returning from his mission, Sean was informed that his wife was dead. At first, Cassidy attempted to escape his despair over this news by throwing himself into his work at Interpol. Eventually, however, the still melancholy Cassidy left Interpol to become a freelance operative and, as time went on, found himself engaged in some criminal activities.[citation needed]

Factor Three

The legal authorities never discovered that Cassidy was guilty of crimes, but the mutant known as the Changeling did, thanks to the technology of the subversive organization of superhumanly powerful mutants and their underlings known as Factor Three. The Changeling contacted Cassidy, whom Factor Three's technology had also identified as a superhumanly powerful mutant, and invited him to join the organization. Cassidy was appalled upon learning of Factor Three's goals and adamantly refused. However, the Changeling and his superior, the so-called Mutant Master, agreed that Cassidy's powers and knowledge of the workings of law enforcement agencies were too valuable for Factor Three to lose, and so they sent their agents to capture Cassidy. Factor Three placed a headband containing explosives around Cassidy's head. If Cassidy defied their orders, the headband could be detonated by remote control; it would also detonate if Cassidy attempted to remove the headband himself. Furthermore, Factor Three put Cassidy, who went by the code name of Banshee, under the supervision of one of their trusted human agents, the Ogre. Banshee thus felt forced to obey Factor Three's commands and, accompanied by the Ogre, performed various criminal missions for the organization.[1]

While in New York City on a mission for Factor Three, Banshee clashed with the original X-Men, who captured both him and the Ogre. The X-Men's leader, Professor Charles Xavier, used a psionic "mental bolt" on Banshee's headband which prevented the detonation mechanism from functioning so that the Banshee could remove it. Once freed of the headband, Banshee told the X-Men all that he knew about Factor Three. Banshee discovered Factor Three's secret European headquarters, only to be recaptured. He participated in the X-Men's battle with the Mutant Master and it was his powers which exposed the Mutant Master as an extraterrestrial.[2]



Banshee returned to an honest life and time passed without major incident for him, except for his brief captivities by the Sentinels, and by the second Secret Empire. Professor Xavier later invited the Banshee to join the X-Men, when he was recruiting new members to battle the menace of Krakoa[3]. After most of the original team left, Cassidy, along with fellow new recruits Colossus, Nightcrawler, Storm, Wolverine, and Thunderbird, stayed as members of the new X-Men. The second group of X-Men were mostly adults and required no tutoring from Professor X, but trained in the use of their powers, in the Danger Room[4]. It was during this time that he met Prof. Xavier's silent partner, the Scottish geneticist Dr. Moira MacTaggert.[5]

Sean was among those captured by Steven Lang's Sentinels and taken aboard Lang's space station.[6] After a trip to Cassidy Keep, they battled Juggernaut and Black Tom.[7]

During a picnic, they briefly battled Weapon Alpha, who accidentally wounded Dr. MacTaggert and enraged Sean.[8] Cassidy and Dr. MacTaggert soon fell in love, but while Cassidy was based at Prof. Xavier's mansion, Dr. MacTaggert was based at her Mutant Research Center on Muir Island off the coast of Scotland.[citation needed]

In Agarashima, Japan they battled Moses Magnum, a criminal mastermind who had been endowed with the psionic power to cause earthquakes. Magnum unleashed tremendous psionic energy in an attempt to create seismic waves great enough to cause a chain reaction that would destroy Japan. Banshee, simultaneously, used his powers to create waves of vibratory force that would cancel out the waves of force that Magnum was creating. Banshee succeeded, to the extent that only small uninhabited islands in the vicinity of Magnum's base were destroyed. However, the tremendous strain that Banshee had placed upon his powers in performing this heroic feat seriously damaged his vocal cords. Cassidy soon regained his ability to speak, but his superhuman sonic powers, which were dependent on his vocal cords, appeared to have been destroyed.[9]

Cassidy accompanied the X-Men to Muir Island where they battled the menace of Proteus, Dr. Moira MacTaggert's mutant son, who at one point took his mother prisoner. Proteus was defeated and the experience of seeing the woman he loved in danger made Cassidy realize that he wanted to stay by her side.[10] Therefore, Cassidy retired from the X-Men and he and Dr. Moira MacTaggert divided their time between Cassidy Keep and Muir Island. Cassidy briefly returned to aid the X-Men against operatives of Arcade, during an emergency situation when Miss Locke kidnapped Dr. MacTaggert and most of the X-Men were simultaneously engaged in conflict with an android which Doctor Doom had created in his own image.[11]

Later, the X-Men battled Black Tom Cassidy, his partner the Juggernaut, and Theresa, who had developed sonic powers of her own, which she used under the alias of Siryn. Theresa felt obliged by her duty toward Black Tom, the man who had raised her (and whom she called "uncle" out of respect, although they were actually cousins), to assist him in his crimes. After they were defeated by the X-Men, Black Tom gave Theresa a letter to Sean, explaining that she was his daughter. Sean and Theresa were joyfully united at Xavier's mansion. Sean was later captured by Thunderbird, brother to the original Thunderbird who blamed Xavier for his brother's death, and was rescued by the X-Men.[citation needed]

Generation X

Hard times with Emma

After rejoining the X-Men as an active member, Banshee suddenly realized the Phalanx's kidnapping of the X-Men. He and Emma Frost worked to save some young mutants targeted by the Phalanx. Banshee later became the co-head master of the Massachusetts branch of the Xavier institute along with Emma Frost, the branch that housed Generation X.[12][13]

Generation X disbanded after Chamber's graduation, shortly after the death of Sean's lover, Moira MacTaggart. Sean became inactive, until he turned back to his alcoholism for a brief period, and then his bitterness towards the mutants who were like those who killed her got to him.[citation needed]


Sean founded X-Corps, a superhuman militia organization that used primarily mind-controlled former terrorist mutants to protect mutant kind at large. Mystique infiltrated the organization in disguise, and slit Cassidy's throat. Luckily, he managed to capture Mystique by releasing Abyss, a mutant who could open an other-dimensional portal.[citation needed]


He did little more without his powers for a long time, until he was asked by the X-Men to go to Muir Island after M-Day to look for any notes that might help find Professor X. Sean uncovered some startling information, and quickly arranged a flight to Westchester.[citation needed]


He was supposed to meet Nightcrawler and Wolverine but noticed that the Blackbird seemed to be heading towards a plane on a collision course. He quickly used his powers to fly and attempted to use his sonic scream to stop the plane from hurting the passengers. Sadly, it was not enough to stop the Blackbird and it rammed into him as well as the plane filled with innocent passengers.[14] Banshee's body was found by Kurt and Logan. When the X-Men were blamed for the situation early on, Emma Frost told O.N.E. that the attack also killed the X-Men's best friend.[15]

Cyclops delivered the news of Banshee's death to his daughter, Siryn.[16] Siryn was given a video tape that Banshee had made for the purpose of delivering a message to his daughter when he died. In the message, Banshee stated that he felt he had done more good than bad in his life, and that he hoped St. Peter would allow him entrance into Heaven. He expressed the hope that he would there be re-united with Siryn's mother. Siryn refused to believe that Banshee was really dead, citing all of the X-Men in the past who have been presumed dead but later returned. Sean willed Siryn Cassidy Keep, as well as his pipe.[citation needed]

He was buried at the Xavier Institute, alongside the empty graves of Sway and Petra Kristensen.[17]

Banshee fights Captain America, Wasp, and Havok


Banshee was seen in Erebus by Hercules along with many other deceased beings, gambling for his soul.[citation needed]

Later, Banshee, along with many other deceased mutants, was resurrected by Selene and Eli Bard with the Transmode Virus.[18] When her plans fell through, Banshee returned to the land of the dead, until the Chaos King waged war on reality and the gates to the Underworld were opened, allowing Banshee and many other deceased heroes to return. Banshee along with his fellow resurrected X-Men Thunderbird, Esme and Sophie Cuckoo, Moira MacTaggert, and three Multiple Men dupes fought the forces of the Carrion Crow, a minion of the Chaos King. After succeeding in their mission to repair Earth's ley lines and defeat the Carrion Crow, Sean returned to the realm of the dead with Moira in his arms.[19]

Banshee back with the X-Men

Horseman of Death

Banshee was brought back to life by the Apocalypse Twins, using both the Life Seed and Death Seed, in order to serve, alongside Sentry, Grim Reaper, and Daken, as one of their Horsemen of Death.[20] Banshee later ended up in the X-Men's custody as Beast concluded that healing Banshee of the Death Seed energy that made him a Horseman of Death would take years and highly advanced technology.[21]

Post Age of X-Man

Sean later resurfaced as part of the Mutant Liberation Front along with Hope Summers.[22]. After a confrontation with the X-Men and newest incarnation of the Brotherhood of Mutants, Sean rejoined the X-Men [23]

When attacking the O*N*E headquarters, he was caught with a huge, big weapon like a hulk killer. The machine caught Banshee and crushed him under its foot. Banshee managed to belt out a final scream which detonated the robot, killing Sean in the ensuing chaos. The X-Men mourned him as they knew the explosion caused his death.[24]

House of X

Sean Cassidy was at some point resurrected by a group of mutants known as “The Five” (Eva Bell, Proteus, Hope Summers, Elixir, and Goldballs), completely cured of the Death Seed energy. He was living on the sovereign nation-state of Krakoa for mutants, created by Charles Xavier, Magneto, and Moira X.[25] He was later seen at the celebration following the recognition of Krakoa as a sovereign nation by the United Nations and the first meeting of the Quiet Council. While partying he shared a knowing look with his daughter Siryn, just before she teamed up with Dazzler to produce a lightshow for the partiers.[26][27]


Banshee is a mutant who possesses unusually strong sonic abilities.

Acoustikinesis: He created powerful sonic waves with his voice with which he could achieve various effects, often with the assistance of psionic abilities which function only in unison with his sonic abilities.

  • Sonic Scream: He had the ability to shatter solid objects with an incredibly loud and destructive sonic scream.
  • Flight: He had the ability to fly at subsonic speeds by using his voice to propel him through the air and ride via sound waves.
  • Sonar: He could use his sonic powers as a form of sonar (Sound Navigation and Ranging). By sending out a precise, pure note and listening to the returning, altered wave-front of the note, he could evaluate his surroundings in total darkness with varying degrees of resolution.
  • Sonic Shield: He could tighten sound waves around himself or others near him, making a barrier against outside attack.
  • Vocal Disorientation: He had the ability to change someone’s balance, by affecting their equilibrium using his sonic scream.
  • Vocal Trance: He had the ability to subtly influence people's subconscious mind by changing the tones and vibrations of his voice using hypersonic suggestions and persuasive abilities.
  • Vocal Unconsciousness: He had the ability to affect the fluid in someone’s ear causing the person to go unconscious.
  • Sound Immunity: Banshee's hearing and equilibrium were unaffected by his hypersonic abilities or other similar sound/sonic-based abilities.
  • Superhuman Vocal Stamina: He possessed superhuman stamina in his lungs, throat, and vocal cords.


A gifted detective, seasoned undercover operative, and unarmed combatant, Sean was also well-versed in combat strategy and tactics. He was an excellent marksman, amateur machine-smith, educator, organizer, and lobbyist. His interests included American country music and playing the piano.

Strength level

Sean Cassidy possesses the normal human strength of a man of his age, height, and weight who engages in moderate regular exercise.


His vocal cords were susceptible to injury from excessive strain in using sonic powers. He had also survived normally fatal throat wounds at the cost of his sonic powers temporarily.


Banshee's Wings: Professor X developed a harness for Banshee's X-Uniform. Using the Harness and his sonic scream he is able to glide on air currents. Using the harness he is able to fly at subsonic speeds.


Flight under his own power; X-Men Blackbird, X-Men Stratojet, Professor Xavier's Rolls Royce.


Conventional firearms, explosive "micro-bombs".

  • When originally created, Roy Thomas and Werner Roth had the Banshee as a female, but Stan Lee told them that female villains were not as popular as male, and she was changed into a male. Roy noted that the way Siryn looked is what Banshee was originally going to look like.
  • Banshee was also immune to his cousin Black Tom's energy blasts.
  • The "ribbons" on Banshee's costume (a visual trademark of the character) aided him in his flight.

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