A former Interpol agent with a unique mutation, Irish-born Sean Cassidy Banshee infiltrates the evil Factor Three but they manipulate him into participating in criminal activities. Freed by Charles Xavier, AKA Professor X, he joins the X-Men and helps them succeed in many battles with his flight and signature sonic scream. He falls in love with X-Men ally and geneticist Dr. Moira MacTaggert, and co-founds the new Generation X with Emma Frost.
Ireland’s storied Cassidy clan is an ancient and noble lineage steeped in heroism, secrets, adventure, feuds, and tragedy, all of which Sean Cassidy inherits in some measure. The family’s ancestral home is Cassidy Keep, a fortress-like castle in a remote, sparsely populated coastal area of County Mayo, overlooking the Atlantic Ocean from high atop the granite cliff Cassidy Crag. The Cassidy presence there predates historical records, and Cassidy Keep itself was built by Liam Cassidy over a thousand years ago to defend the Irish coast against Viking raiders. The Keep also covertly sheltered the “Families” (diminutive, enchanted leprechauns or elves). In recent decades, the castle’s Seneschal or steward, Eamon O’Donnell, serves as both caretaker of Cassidy Keep and guardian of the “Families.”
Born and raised in Cassidy Keep, Sean Cassidy has a happy boyhood, fantasizing about fighting dragons and rescuing damsels. During adolescence, Sean discovers his mutant sonic powers but conceals them—partly because his wail spooked the superstitious elders of the community, who likened it to the ghostly banshees of Irish lore.
Banshee’s superhumanly powerful lungs, throat, and vocal cords could produce a sonic scream for various effects, in concert with limited, reflexive psionic powers that direct his sonic vibrations. He can hover or fly at the speed of sound and can carry at least one passenger. He can overwhelm listeners with deafening noise, stun them with tight-focus, low-frequency sonic blasts, effective even against shielded ears by penetrating the skull via bone conduction. He can plunge listeners into a hypnotic trance, disorient them, nauseate them, or simply render them unconscious.
Using sonic waves, he can rapidly vibrate himself or other masses at will. He can generate sonic blasts, which strike with tremendous concussive force, liquefying or outright disintegrating targets at his highest levels of power. By radiating sound waves outward and reading the feedback, he can locate and analyze unseen objects in a sonar-like fashion. By modulating his scream’s harmonics, he can confuse most scanning equipment. He can instinctively analyze, replicate, and block sonic waves or vibrations from other sources.
Banshee generates a psionic field, which protects him from the detrimental effects of his sonic vibrations, though his sonic powers can still injure him when pushed beyond safe limits. His physiology seems fully vulnerable to conventional injury when his sonic powers are not engaged.
Banshee has selective hearing, enabling him to focus upon, enhance, or totally block out any given sound in his environment; this shields him from the deafening sound of his own screams, and makes him a superhumanly acute eavesdropper in surveillance situations.
Sean and his cousin Thomas Cassidy, AKA Black Tom Cassidy, are immune to each other’s natural mutant energy powers. A gifted detective, veteran undercover operative, and formidable unarmed combatant, Cassidy is an excellent marksman and a competent amateur machine smith, well-versed in combat strategy and tactics and teamwork drills. An effective educator, organizer, and lobbyist, he is also an avid American country music aficionado and skillful amateur piano player.
As Cassidy, he wields conventional firearms and sometimes carries explosive “micro-bombs.” As Banshee, he wears synthetic costuming designed to resist air friction, usually including underarm wings that help him glide on air currents and his own sonic waves.
Sean’s cousin, “Black Tom” Cassidy, became his lifelong rival. Like Sean, Tom was secretly a mutant; Tom was also a gambling man who loved to live dangerously. Tom was next in line to inherit the Cassidy estate and its modest wealth but gambled away these rights to his cousin Sean in an ill-advised wager. Despite this setback, Tom remained a suave, charming, Oxford-educated ladies’ man, often making the less cultured Sean feel like a hapless country bumpkin by comparison. As young adults, the cousins competed for the affections of Maeve Rourke, whom Sean met in Northern Ireland.
Family Ties and X-Men Allies
Sean’s relationship with Maeve Rourke starts out rocky with his cousin vying for her attention, but Maeve ends up choosing Cassidy. They marry and have a daughter, Theresa Rourke Cassidy, AKA Siryn. Though he loses them both in a terrorist bombing. Little does he know that Theresa survives and is taken in by Black Tom, who adopts her, and keeps her existence secret.
With an interest in law enforcement, Sean joins the NYPD and Interpol, even acting as a spy in the subversive organization Factor Three. After taking the codename Banshee, Sean joins several mutant teams including the X-Men, X-Corps, Generation X, and the Mutant Liberation Front, proving to be a hero helping to fulfill Xavier’s dream of peaceful coexistence with humans.
Through the X-Men’s leader Professor X, Sean meets geneticist Moira MacTaggert and they share a long-lasting romance.
Scream Like a Banshee
One night, Sean hitchhiked home from a concert when he was harassed by corrupt policeman Sergeant McLanahan, who seemed keen on arresting Sean as a supposed terrorist, despite lacking evidence. A passing motorcyclist, Maeve Rouke, rescued Sean, but McLanahan chased them across the Irish border and sent their motorcycle off a cliff, forcing Sean to use his sonic scream to fly himself and Maeve to safety. Sean took Maeve back to Cassidy Keep, where she adapted surprisingly quickly to her discovery of Sean’s bizarre powers. She just as quickly grew fond of both Sean and his charming cousin Tom, each of whom was quite smitten with her. Maeve dated both cousins for months, apparently genuinely torn between the two, but chose Sean as her escort for the university ball.
Badly injured when a vengeful McLanahan ran him off the road en route to the university, Sean sent Tom to escort Maeve in his place. Tom initially offered no explanation for Sean’s absence, and the disappointed and puzzled Maeve accompanied Tom to the dance; but Tom, unable to lie to her, eventually confessed Sean’s true circumstances. Touched by the gesture, Maeve called Tom her dearest friend, though her heart clearly belonged to Sean. Stepping aside gracefully, Tom later served as best man at their wedding; but losing Maeve to Sean accelerated Tom’s gradual, secret descent into immoral, dangerous, and increasingly criminal acts as he dabbled in mercenary work and various illegal ventures. Sean, meanwhile, graduated from Trinity College with a science degree and went into law enforcement.
Well over two decades ago, he became an agent of the international police organization Interpol. As a rookie agent, Cassidy failed to prevent the terrorist organization Hydra’s enslavement of weapons specialist Patrick Lipton, whom Cassidy subsequently believed dead. Later, Cassidy hunted down the Russian mutant serial killer Arkady Rossovich (the future Omega Red) with the aid of Max Eisenhardt, AKA Magneto, and Interpol colleague Magrite Deveraux, who was slain by Rossovich. He also teamed with fellow agent Daniel Peyer to infiltrate the offices of mob boss Almadovar until the mercenary Wade Wilson, AKA Deadpool, interfered, saving Sean’s life but ruining the operation by killing Almadovar.
While Sean was on a long-term deep cover assignment that kept him away from home with no contact for many months, Maeve gave birth to their baby daughter Theresa; but mother and child were soon caught in a terrorist bombing and apparently killed. Sean had not known Maeve was pregnant, and the few who knew about the newborn baby decided it was better to conceal her existence from Sean, lest it cause him further pain. Theresa secretly survived, was rescued and adopted by her “uncle” Tom. When Sean finally returned and learned of Maeve’s death, Tom considered telling his cousin the truth about Theresa; but a grief-crazed Sean lashed out at Tom, blaming him for not protecting Maeve in his absence, and accidentally gave Tom a crippling leg injury.
Further embittered, Tom decided to raise Theresa himself in secret. Sean became an obsessive workaholic and, perhaps hoping distance would help ease the pain, he briefly transferred to the NYPD in New York City, where he once aided young mutant telepath Emma Frost while he and his partner Lowell Fontaine were running surveillance of wealthy criminal Harry Leland (though Frost mind-wiped Cassidy’s memory of the incident).
He soon rejoined Interpol and encountered the mutant brawler Logan/James Howlett, AKA Wolverine, while apprehending criminals in Calgary, Alberta. After years of international assignments, Sean came home and led an undercover operation targeting his cousin, Black Tom, by now a major criminal. Tom was soon sentenced to life in prison, but Theresa remained unaware of her true parentage since Tom had long since sent her to a distant private school to shield her from his darker dealings. Apparently by now aware of Sean’s mutant powers—perhaps due to an investigation of Cassidy’s exploits by the Weird Happenings Organization (W.H.O.)—Interpol sent Sean back to America to infiltrate the rising mutant subversive organization Factor Three.
The increasingly disenchanted Sean, still mourning Maeve, quit Interpol for good and became a freelancer, secretly dabbling in minor crimes. Ironically, this attracted the attention of Factor Three (mostly mutant criminals themselves), and their deputy leader Kevin Sidney, AKA Changeling, tried to recruit Cassidy. When Sean refused, they forced him to wear a remote-controlled explosive headband, which would detonate if tampered with. Thus enslaved, Cassidy, codenamed Banshee, performed criminal missions for Factor Three under the supervision of their loyal agent Ogre, a gifted human machine smith. In a bitter twist, Cassidy soon found himself on Interpol’s wanted list. Banshee and Ogre were ultimately defeated by the X-Men, who freed a grateful Banshee from Factor Three’s service. Cassidy later helped the X-Men bring down Factor Three and exposed its “Mutant Master” leader as an extraterrestrial, prompting the defeated villain to kill himself. Banshee kept a low profile thereafter, apart from escaping the anti-mutant Sentinel robots with the aid of the X-Men, and skirmishing with Steve Rogers, AKA Captain America and Sam Wilson, AKA Falcon, while fleeing the mutant-hunting Secret Empire.
A diehard country music fan, Cassidy was in Nashville, Tennessee when Professor X recruited Sean and several other mutants to form a new squad of X-Men to rescue the previous X-Men from the living island Krakoa. After the successful completion of this mission, Banshee considered leaving, since he felt too old for the mostly youthful group, but Xavier and team leader Cyclops convinced him to stay. During an early mission, Sean saw his reckless teammate John Proudstar, AKA Thunderbird, killed in action; though haunted by this loss, Sean soon settled comfortably into life with the X-Men. Being of similar age, he sometimes served as a confidant of sorts to Xavier; and being one of the new team’s more experienced and stable members, he occasionally assumed an informal leadership role in the absence of Xavier and Cyclops. The team’s foremost foe, Sean’s former ally Magneto, once referred to the formidable Banshee as the only worthy opponent among the new X-Men.
Sean also began a long-running romance with Xavier’s silent partner, geneticist Moira MacTaggert. When Sean finally inherited his family’s estate, he and the X-Men were ambushed at Cassidy Keep by a vengeful Black Tom and his new ally Cain Marko, AKA Juggernaut, both of whom had been paid to destroy the X-Men by Shi’ar agent Eric the Red. The X-Men defeated the villains with the aid of Cassidy Keep’s leprechauns. After many more adventures with the X-Men, Banshee burned out his sonic powers while saving Japan from destruction by Moses Magnum. He continued to assist the X-Men as best he could, notably aiding them against Moira’s murderous mutant son, Kevin MacTaggert, AKA Proteus.
Realizing his injuries might be permanent and knowing Moira needed him, Sean retired from the X-Men and moved into Moira’s Muir Island research complex, where he convinced a grieving Moira to abandon plans to resurrect her monstrous son. Cassidy lived a mostly quiet life for the next several years, though his lack of super-powers did not stop him from joining a successful mission to rescue Moira and other X-Men associates from Murderworld. He continued to assist the X-Men on occasion in various support capacities; through them, he finally met his daughter Theresa, now the young adventurer Siryn. Her true parentage was belatedly revealed to both Sean and Theresa by Black Tom. It was a joyful discovery for both, though Sean’s complete absence from Theresa’s early life occasionally made their relationship an uneasy one. A new James Proudstar, AKA Thunderbird, brother of the original, mistakenly blamed the X-Men for his sibling’s death and kidnapped Sean to lure the X-Men into a trap. He ultimately found himself incapable of killing and relented, parting with the X-Men on civil terms. Ironically, Proudstar and Siryn would later become close friends while serving together in X-Force.
When the robotic Master Mold mind-controlled Moira into creating the mutant-killing Retribution Virus, Sean was afflicted by it; however, an antidote created by Moira not only saved his life, but also restored his powers to some extent, and he helped Cyclops defeat Master Mold. Later, when Sean was shot during the cyborg Reavers’ assault on Muir Island, the Morlock Healer healed Sean’s wound, also restoring his powers to their peak. After helping repel the Reavers alongside a makeshift roster of substitute X-Men, Banshee teamed with Forge to search the world for the core X-Men, who were missing and mistakenly presumed dead. During this period, the Irish government’s new super-agents, the Kinsmen, came to Cassidy Keep to recruit Banshee into their ranks and force him to submit to a long-overdue debriefing; but Siryn single-handedly sent the unfriendly visitors packing. Thanks in part to Forge and Banshee, the X-Men gradually reassembled. Sean rejoined the group, notably helping liberate Muir Island and its inhabitants from the Amahl Farouk, AKA Shadow King. Sidelined by a broken jaw, Banshee sought out a distraught Moira, who was coping with guilt over her long-ago genetic alterations of Magneto.
After a healed Sean rejoined the team, becoming concerned about the welfare of largely unsupervised junior member Jubilation Lee, AKA Jubilee, he helped secure treatment for a mutating Black Tom, aided Deadpool in dodging the vendetta of vindictive Interpol agent Daniel Peyer, and learned of Patrick Lipton’s survival just in time to attend Lipton’s deathbed. Banshee soon teamed with Jubilee, former villain Emma Frost and a reluctant Victor Creed, AKA Sabretooth, to rescue a group of mutant teens from the extraterrestrial Phalanx. One of the teens, Clarice Ferguson, AKA Blink, sacrificed herself to make the victory possible. The survivors, Jubilee and various other young mutants all enrolled in Xavier’s new youth education program at the Massachusetts Academy, with Sean and a newly reformed Emma as co-headmasters. Cassidy and Frost worked together uneasily at first, and experienced several severe fallings-out, but gradually forged a mutually respectful working relationship and a strong bond with their students, Generation X.
Family troubles would continue to haunt Sean, though—Generation X once rescued Cassidy Keep from displacement in another dimension, and Black Tom attacked the group several times over. Banshee’s lover Moira placed herself in quarantine after contracting the Legacy Virus, and she eventually died when Raven Darkhölme, AKA Mystique, bombed Muir Island. Sean took the news hard and began drinking heavily. This alcoholic downslide, combined with Emma’s wavering morality, funding troubles, and other factors, led to the disbanding of the Generation X program. Sean retreated to Ireland, quit drinking, and channeled his grief into an obsessive new mission: Creating and leading the international paramilitary mutant police force known as the X-Corps. Using funds from a forgotten Factor Three account and various criminal accounts frozen by Interpol and basing the group in an abandoned Advanced Idea Mechanics (A.I.M.) facility stocked with highly advanced equipment, Banshee recruited various volunteer mutant adventurers (including former Generation X students) and pressed criminal mutants into X-Corps service through the mental powers of captive criminal mutant mentalist Jason Wyngarde, AKA Mastermind.
Designed to self-police the mutant community, the X-Corps rapidly became a respected and feared presence in Europe sanctioned by various authorities, but the X-Men voiced concerns regarding the group’s sometimes questionable methods and Banshee’s uncharacteristically ruthless attitude (possibly influenced by Mastermind, who was secretly undermining the group on behalf of Mystique). The X-Men’s fears proved well-founded when Mystique infiltrated the group, freeing the criminal members from Banshee’s control, slitting Banshee’s throat, and trying to take over the Corps. The X-Men and the benevolent members of X-Corps soon halted the freed criminals’ rampage, and a wounded Banshee managed to defeat Mystique with the aid of Nils Styger, AKA Abyss. Unfortunately, several X-Corps members were apparently slain, the city of Paris was devastated, and Banshee was again stripped of his sonic power by his injuries.
After a lengthy hospital stay, Sean went into seclusion and the remnants of his X-Corps were taken over by Xavier to form the search-and-rescue X-Corporation. Sean had barely begun to heal, both emotionally and physically, when he uncovered vital information regarding the X-Men’s dangerous new enemy Gabriel Summers, AKA Vulcan. Unwilling to entrust this information to electronic communication, Cassidy flew back to America via commercial aircraft, but Vulcan seized control of the X-Men’s Blackbird jet and set it on a collision course with Sean’s plane. Healed enough to fly short distances under his own power, Banshee exited the plane and could have flown to safety, but instead tried to save his fellow passengers by sonically deflecting the Blackbird; however, the injured Banshee lacked the power to accomplish this feat and was caught between the two planes in a fiery mid-air explosion, sacrificing himself to protect innocent human lives. His last will and testament left Theresa the Cassidy Keep estate and his favorite smoking pipe, an old family heirloom signifying Sean’s love for his daughter and her role as the Cassidy legacy’s true heir.
Though Banshee’s story continued when he was resurrected by Selene and Eli Bard who used the Transmode Virus. Though controlled, he fought back and attempted to contact Emma and Scott to warn them, but his captors caught him before he could warn them. After Selene’s plot failed, Banshee returned to the Underworld. When the Chaos King chased the dead from the Underworld, a team of dead X-Men including Banshee, Thunderbird, telepaths Esme and Sophie Cuckoo, of the Stepford Cuckoos, Moria MacTaggert, and Jamie Madrox, AKA Multiple Man, rose to oppose his minion and demonic Carrion Crow, a corrupted Native American God. But one of their own, Sophie, sacrificed herself to allow the others to escape the Crow.
As they recovered, Esme contacted her sister telepathically and fought her, turning into a crow herself. A battle followed with the Carrion Crow. All the Madrox duplicates got taken down and Banshee gets clipped by an energy-band emanating from the Crow. Moira, weakened for some reason, directed Banshee to blast the Carrion Crow and destroy the portal he had created, which negatively impacted the Earth’s laylines. Banshee’s sonic blast disables the demon and shatters the portal. The blast brought down the Cuckoo sisters for a moment but started to battle each other. As Thunderbird reached out to his god for aid, Banshee blasted Carrion Crow with all a sonic scream and protected Moira. It wasn’t enough and they were slain, despite already being dead, by Carrion Crow, leaving Thunderbird alone to defeat him. Thunderbird beseeched the spirits and with their help healed the Earth’s laylines from the demon’s destruction and restored order to the Underworld.
Banshee later returned to life thanks to the Apocalypse Twins who used the Life Seed and the Death Seed to do so. As their Horseman of Death, he served them with Akihiro, AKA Daken, Eric Williams, AKA Grim Reaper, and Robert Reynolds, AAK Sentry. When Banshee was captured by the X-Men, it was Hank McCoy, AKA Beast, who thought he could be healed but it would take many years and more advanced technology.
While he was kept in a coma, the Reavers came upon him and forced Beast to release Banshee. He was infected by Skullbuster which allowed him to be in control of himself, but it didn’t last long and his sonic screams were uncontrollable. Dazzler defeated him by absorbing his screams and defeated the Reavers as well. Coming to, Banshee expressed that he wanted to help himself.
He joined the Mutant Liberation Front alongside Hope Summers. After going head-to-head with the X-Men and battling the Brotherhood of Mutants, Cassidy ultimately rejoined the X-Men. Later, while up against a giant Sentinel and stuck underfoot, Banshee released a scream that exploded it into oblivion.
After Xavier, Magneto, and Moira created the mutant nation-state Krakoa, they gathered a group of mutants who could resurrect fallen brethren. They were known as The Five and one of their resurrected included Banshee. Cassidy was cured from the effects of the Death Seed and became his old self. He chose to live on Krakoa where his daughter Siryn lived as well.