History: Sean was born in Ireland, heir to Cassidy Keep. Eventually joining Interpol he quickly rose through the ranks. On one mission for Interpol he was forced to stay out of Ireland for a long time. It was during this time that his wife, Maeve, gave birth to their daughter Theresa. Maeve was later killed in a terrorist bombing in Armagh and it was thought that baby Theresa also died. Sean's family and friends decided not to tell him of Theresa's existance, hoping to spare him more pain. However, Black Tom had rescued the child from the explosion and raised her. Banshee left Interpol and became a free agent. He eventually came in contact with the organisation known as Factor Three who placed a control collar on him which would explode if he didn't follow their orders. He helped them in their criminal activities until they battled the X-Men. Professor Xavier used a psionic bolt on Banshee which deactivated the collar. He then helpd the X-Men capture Factor Three. Sean returned to a normal life until called upon by Prof. X to join the second wave of X-Men who were needed to rescue the original memberss from Krakoa, the living island. Banshee lost his mutant abilties after battling Moses Magnum and retired.
Later the X-Men battled, and defeated, Black Tom, his partner Juggernaut and Theresa, who had aided her cousin in his criminal activites under the name Siryn. Black Tom wrote a letter that exonerated Theresa from blame for the crimes she had aided him in as well as explaining to Banshee what had happened to Theresa. Father and daughter were reunited.
Sean is now co-headmaster at the Massachusetts Academy where he teaches Generation X, the newest generation of mutants, alongside Emma Frost. During his time as headmaster, Black Tom Casssidy has attacked twice.
Although Sean has usually been portrayed as the friendly uncle-type mentor he began to take a harder, more pro-active line with the GenX kids after the death of Synch.
Sean returned to Ireland when the Academy closed.
Strength level: Normal strength for a man his age, weight and height who engages in regular exercise.
Flight speed: Speed of sound.
Stamina: (lungs, throat, vocal cords) superhuman.
Stamina: (rest of body) athlete.
Known superhuman abilities: Banshee can create sonic waves with his voice which can enable him to fly, shatter solid objects, put people in a state of hypnosis or cause people to fall unconscious.