Real Name: Sean Cassidy
Occupation: (Currently) Founder and directory of operation for X-Crops, (formerly) Adventurer and Headmaster at the Massachusetts Academy, in charge of Generation X, Interpol Inspector and Agent, freelance detective, professional criminal, involuntary operative for Factor Three
Legal Status: Citizen of the Republic of Ireland with no criminal record
Identity: Secret
Place of Birth: Cassidy Keep, Ireland
Marital Status: Widower
Known Relatives: Maeve Rourke Cassidy (wife, deceased), Thomas (known as "Black Tom," cousin), Theresa Rourke (alias Siryn, daughter)
Group Affiliation: (currently) X-Corps (formerly) Generation X, Factor Three, X-Men
Base of Operations: (formerly) Massachusetts Academy; Professor Xavier's School for Gifted Youngsters, Salem Center, Westchester County, New York State; and Cassidy Keep Ireland and Muir Island, off the coast of Scotland
First Appearance: X-MEN (first series) #28

History: 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.

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 Rourke, before she ultimately married Sean.

Sean Cassidy 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 Tom nor Maeve knew it at the time. Their daughter, Theresa, was born during Sean's absence. 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 by an explosion caused by terrorists. No trace of Theresa was found by the authorities, and they and Maeve's relatives assumed that Theresa had also been killed in the explosion. 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.

On returning from his mission, Sean Cassidy was informed that his wife was dead. Those who knew that Theresa had been born decided not to inform Sean Cassidy that Maeve had had a daughter in order to spare him further grief. 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, he found himself engaged in criminal activities. 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 had a headband containing explosives placed 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. The Banshee thus felt forced to obey Factor Three's commands, and, accompanied by the Ogre, performed various criminal missions for the organization.

While in New York City on a mission for Factor Three, the 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 the Banshee's headband which prevented the detonation mechanism from functioning so that the Banshee could remove it. Once freed of the headband, the Banshee told the X-Men all that he knew about Factor Three. Later, the Banshee discovered Factor Three's secret European headquarters, only to be recaptured. But the Banshee participated in the X-Men's battle with the Mutant Master, and it was the Banshee's powers which exposed the Mutant Master as an extraterrestrial.

The 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. The Banshee remained in the X-Men for some time. It was during this time that he met Xavier's silent partner, the Scots geneticist Moira MacTaggert. Cassidy and MacTaggert soon fell in love, but while Cassidy was based at Xavier's mansion, MacTaggert was based at her mutant research center on Muir Island off the coast of Scotland.

While in Japan the X-Men found themselves in battle with Moses Magnum, a criminal mastermind who had been endowed with 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. The Banshee simultaneously used his powers to create waves of vibratory force that would cancel out the waves of force that Magnum was creating. The Banshee succeeded to the extent that only small uninhabited islands in the vicinity of Magnum's base were destroyed. However, the tremendous strain that the 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.

Cassidy accompanied the X-Men to Muir Island where they battled the menace of Proteus, 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. Therefore, Cassidy retired from the X-Men, and he and 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 most of the X-Men were simultaneously engaged in conflict with an android which Doctor Doom had created in his own image.

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 are 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.

Banshee is now the co-headmaster at the Massachusetts Academy, where he teaches young mutants in the use of their powers alongside Emma Frost.

Height: 6 ft.
Weight: 170 lbs.
Eyes:Blue-green
Hair: Blond

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

Flight Speed: Speed of sound

Stamina: (lungs, throat, vocal cords) Superhuman, (rest of body) Athlete

Known Superhuman Powers: Sean Cassidy is a mutant who has the same powers as his daughter Siryn, but who cannot use them in as many ways as she can. His powers function in the same way that hers do: he creates powerful sonic waves with his voice with which he can achieve various effects, often with the assistance of limited psionic abilities which function only in unison with his sonic power. The Banshee can use his sonic powers to propel himself through the air in flight, to shatter solid objects, to place human beings temporarily into a hypnotic trance, or to cause human beings to fall temporarily unconscious.

Special limitations: Vocal cords susceptible to injury from excessive strain in using sonic powers.

NOTE: Jeremy Ratchford played him in Generation X made for T.V. movie.