Banshee first appeared in X-Men #28, published in January 1967. He was co-created by writer Roy Thomas and artist Werner Roth. His introduction came during a period when the X-Men's roster was still in its early stages of development, and new mutants, both friend and foe, were frequently introduced to expand the world. Initially, Sean Cassidy was not presented as a hero. He debuted as an antagonist, albeit an unwilling one, controlled by the villainous organization known as Factor Three through a headband containing explosives. They forced him to carry out their criminal activities, bringing him into direct conflict with Charles Xavier's original X-Men. This “reluctant villain” trope was common in the Silver Age, allowing for a character to showcase their power set against the heroes before a reveal that redeems them. After the X-Men freed him from Factor Three's control, he became a firm ally. He wouldn't become a full-fledged member of the team, however, until the landmark relaunch in 1975's Giant-Size X-Men #1, where he was recruited alongside characters like Wolverine, Storm, and Colossus to form the “All-New, All-Different” X-Men. This cemented his place as a cornerstone character for a new era of mutant stories.
The in-universe origin of Banshee is a story marked by tragedy, duty, and the slow acceptance of an extraordinary power. His journey differs dramatically between the core comic continuity and his cinematic adaptation.
Sean Cassidy was born in Cassidy Keep, County Mayo, Ireland, the heir to a small fortune and an ancestral castle. He led a relatively normal life for many years, eventually joining the international law enforcement agency, Interpol, as a detective. During his time with Interpol, he married Maeve Rourke, and they were expecting their first child. While on a deep-cover mission, Sean was out of contact for an extended period. During his absence, Maeve gave birth to their daughter, Theresa. Tragically, Maeve was killed in an IRA bombing shortly after. Sean's cousin, the nefarious Black Tom Cassidy, was present and, out of a long-standing familial rivalry and jealousy, took custody of Theresa. When Sean returned, Black Tom told him that both Maeve and the child had died, leaving Sean devastated and unaware he had a living daughter. The trauma and stress of these events likely triggered the full manifestation of Sean's latent mutant powers: his sonic scream. Unable to control it at first, he was forced to wear a special suit to dampen the effects. This power brought him to the attention of Factor Three, who captured him and dubbed him “Banshee” after the wailing female spirit of Irish folklore. They used a mind-controlling device to force him to serve their agenda, which led to his first confrontation with the x-men. Professor Charles Xavier was able to use his telepathy to help Sean break free of the control, and together they defeated Factor Three. Grateful but still a loner, Sean went his own way for several years. His path crossed with the X-Men again when Xavier sought him out to join a new international team of mutants to rescue the original X-Men from the living island, krakoa. At this point, Sean was older and more experienced than the original team members, bringing a level of maturity and worldliness to the new roster. He accepted, becoming a stalwart member of this new generation of X-Men and finding a new family among them.
Banshee has not appeared in the Marvel Cinematic Universe (MCU). His only live-action appearance is in the 20th Century Fox film, X-Men: First Class (2011), which exists in a separate timeline. This version of the character is a radical departure from the comics. Portrayed by Caleb Landry Jones, Sean Cassidy is depicted as a young, American (not Irish) mutant recruited in 1962 by Charles Xavier and Erik Lehnsherr. He is insecure and struggles immensely with his powers, which manifest as a high-frequency shriek that he cannot properly control. He is part of the first class of “X-Men,” alongside other young recruits like Havok, Beast, and Mystique. His origin is tied directly to the formation of the X-Men. Instead of a seasoned Interpol agent with a tragic past, he is a “work in progress,” a student learning from his mentors. A key sequence in the film involves Charles Xavier and Erik Lehnsherr training him to master his abilities. He learns to focus his sonic screams into concussive blasts and, in a triumphant moment, masters the ability to fly by using his own sound as propulsion, a direct and visually spectacular nod to his comic book abilities. He plays a crucial role in the film's climax during the Cuban Missile Crisis, using his sonar abilities to locate Sebastian Shaw's hidden submarine. This version of Banshee represents a common adaptation strategy in superhero films: de-aging a character to create a coming-of-age arc that can run parallel to the main plot. While he survives the events of First Class, his fate is unceremoniously revealed in the sequel, X-Men: Days of Future Past (2014). It is stated that he, along with other members of the original team like Angel Salvadore and Azazel, was captured, experimented on, and killed by Bolivar Trask's scientists as part of the research that led to the creation of the advanced Sentinels.
Sean Cassidy is an Alpha-Level Mutant whose primary power revolves around the generation and manipulation of sound through his superhumanly powerful vocal cords.
Sean Cassidy is often portrayed as the heart and soul of the teams he is on. He is warm, charming, and possesses a classic Irish wit, often quick with a story or a song. Having lived a full life before becoming a superhero, he carries a maturity and perspective that younger teammates lack. He is a deeply loyal friend and a paternal figure, fiercely protective of those he considers family, especially his daughter Theresa and the students of Generation X. However, his life of tragedy—the loss of his wife, the long separation from his daughter, and the death of his love, Moira MacTaggert—has left him with a deep well of melancholy. He has struggled with alcoholism and periods of self-doubt, particularly when his powers have waned or been lost. This blend of worldly charm and hidden sorrow makes him one of the most relatable and human members of the X-Men.
The cinematic Banshee showcases the same core power set, but from the perspective of a novice learning to control them for the first time.
This version of Banshee is defined by his youth and inexperience. He is initially timid and overwhelmed by his abilities. He is part of a cohort of young mutants who find a sense of belonging and purpose under Xavier's tutelage. He is more of a follower and a student than the leader and mentor seen in the comics, providing a distinct “rookie” perspective within the newly formed team.
Dr. Moira MacTaggert was the love of Sean's life. A world-renowned geneticist and a key human ally to the X-Men, Moira and Sean shared a deep, abiding romance that spanned decades. Their relationship was one of intellectual equals and profound emotional connection. Muir Island, Moira's research facility in Scotland, often served as a second home for Sean. Her death at the hands of Mystique was a devastating blow from which he never fully recovered, sending him into a period of deep depression and alcoholism. In the modern Krakoan era, her resurrection as a mutant with reincarnation powers has dramatically and tragically reshaped their entire history.
For years, Sean believed his daughter, Theresa, had died at birth with his wife. The discovery that she was alive and had inherited his sonic powers was a monumental moment in his life. Raised by his cousin Black Tom, Theresa initially had a strained relationship with the father she never knew. Over time, they grew incredibly close, forming a powerful father-daughter bond. She followed in his footsteps, joining X-Factor and other mutant teams under the codename Siryn, and has now taken up the mantle of Banshee herself.
Sean's relationship with Professor X was built on mutual respect between peers. Unlike the other members of the “All-New, All-Different” team, Sean was of a similar age to Charles and had a comparable level of life experience. He trusted Xavier's dream but was never a blind follower, willing to question and challenge the Professor's decisions when he felt it was necessary. He served as a loyal and capable field leader for the X-Men on numerous occasions.
Banshee and the former White Queen of the Hellfire Club were an unlikely pair. They came from opposite ideological worlds but were thrown together as the co-headmasters of Generation X. Their partnership was fraught with tension, mistrust, and witty banter, but it was also surprisingly effective. They developed a grudging respect for one another, both genuinely caring for their students' well-being, even if their methods clashed. This relationship showcased Sean's ability to find common ground with even his former enemies for a greater good.
Sean's cousin, Black Tom, is his primary and most personal antagonist. Their rivalry stems from a family feud over the Cassidy Keep inheritance and Tom's unrequited love for Maeve, Sean's wife. Black Tom's powers—the ability to project concussive blasts through wood—and his long-standing criminal partnership with the unstoppable juggernaut have made him a persistent and dangerous foe for both Banshee and the entire X-Men team. Their battles are always deeply personal, fueled by decades of jealousy and betrayal.
This landmark issue marks Banshee's official entry into the X-Men. When the original team is captured by Krakoa, Charles Xavier recruits a new, international team to rescue them. Banshee, with his powerful sonic abilities and worldly experience, is a key recruit alongside Wolverine, Storm, Colossus, Nightcrawler, Sunfire, and Thunderbird. His ability to fly and map the island with his sonar was instrumental to the mission's success. This story cemented his place as a core member of the most popular X-Men lineup in history.
When the techno-organic Phalanx targeted the next generation of mutants, Banshee teamed up with Emma Frost, Jubilee, and Sabretooth to save them. The successful rescue of these young mutants—including Husk, Skin, M, and Synch—led directly to the formation of a new school and team. Charles Xavier asked Sean and Emma to serve as co-headmasters of the Massachusetts Academy, the new home of Generation X. This entire era, spanning over 75 issues, was a defining period for Banshee, shifting his role from active field operative to mentor and teacher, shaping the future of mutantkind.
This storyline revealed a long-buried secret: Xavier had sent a secret, second team of young mutants to rescue the original X-Men from Krakoa before recruiting Banshee's team. This secret team perished on the mission. Years later, the powerful and vengeful sole survivor, Vulcan (the third Summers brother), returned. Banshee, who had lost his powers at the time, discovered Vulcan's plan to attack an airplane carrying Xavier. In a final act of heroism, Sean used his latent sonic abilities to create a “sonic sculpture” of a jet to divert Vulcan's attention. While he succeeded in saving the passengers, the effort left him vulnerable, and Vulcan brutally murdered him in mid-air. His death was a shocking and heroic sacrifice that resonated throughout the mutant community.
Years after his death, Banshee's body was stolen by the Apocalypse Twins, Uriel and Eimin. They used a Celestial Death Seed to resurrect him as one of their new Horsemen of Death. Twisted into a horrifying, pale version of his former self, he was forced to fight his former friends and allies, including the Avengers. He was eventually defeated and taken into custody by the Avengers. It took the combined efforts of the X-Men's top scientists to finally purge the Death Seed's influence, though the experience left him physically and psychologically scarred.