- "This old dog's learnt ev'ry new trick in the book!"
Sean Cassidy was born as the heir to the castle and estate of Cassidy Keep, Ireland, as well as a small fortune. Cassidy discovered his mutant powers in his adolescence, but kept them a secret. However, Cassidy's powers were known to his disreputable older half-brother Tom Cassidy, who had discovered that he himself was a superhumanly powerful mutant. Sean and Tom had long been rivals, but it got excessively worse in college, as they were both in love with Maeve Rourke, a fellow college student of theirs. She ultimately married Sean and together they had a son, Sheamus. After graduating from Trinity College, Dublin, with the degree of Bachelor of Science, Cassidy became a detective at Interpol, the international law enforcement organization, though he kept his powers hidden from the rest of Interpol.
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 Tom nor Maeve knew it at the time. Their daughter, Theresa, was born during Sean's absence. Maeve took her son Sheamus, and 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 Maeve was found by the authorities, and they and Maeve's relatives, assumed that Theresa and Sheamus had also been killed in the explosion. In fact, however, Black Tom Cassidy had been present at the scene of the explosion and secretly helped save Sheamus and little baby, Theresa.
On returning from his mission, Sean was informed that his wife and son were dead. Those who knew that Theresa had been born decided not to inform Sean 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 began dating Moira Kinross. However, as time went on, he found himself engaged in criminal activities and the two broke up.
The legal authorities never had proof that Cassidy was guilty of crimes, but was fired from his job and became a heavy drinker. Eventually, Sean was found by the Mutant Magneto who invited him to join the Brotherhood. Cassidy was appalled upon learning of the Brotherhood's goals and adamantly refused. However, Magneto claimed that his son was still alive and said that he would tell him where he was in exchange for his membership. Wanting to see his son more than anything, Sean felt as though he had no choice but to accept.
After helping the Brotherhood on several occasions and still with little to no answers regarding his son, Sean threatened to quit. Magneto didn't like this and threatened Sean himself telling him "I don't think your children would appreciate seeing their father's dead body". This severely angered Banshee, and he pressed Magneto on the plural children. Magneto told him he would reveal everything once he returned from his final mission for the Brotherhood, to go the Xavier Institute For Gifted Youngsters and destroy Cerebro.
Powers and AbilitiesEdit
Sound Manipulation Banshee creates powerful sonic waves with his voice with which he can achieve various effects, often with the assistance of psionic abilities which function only in unison with his sonic power.
- Sonic Scream: ability to shatter solid objects with a sonic scream.
- Flight: ability to fly at subsonic speeds by using his voice to propel him through the air and ride the sound waves.
- Sonar: can 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 wavefront of the note, he can evaluate his surroundings in total darkness with varying degrees of resolution.
- Sonic Shield: can tighten sound waves around himself or others near him, making a barrier against outside attack.
- Vocal Disorientation: ability to change someone’s balance, by affecting their equilibrium using his sonic scream
- Vocal Trance: ability to subtly influence people's subconscious mind by changing the tones and vibrations of his voice using sonics
- Vocal Unconsciousness: ability to affect the fluid in someone’s ear causing the person to go unconscious.
- Sound Immunity: Banshee's hearing and equilibrium are unaffected by his power or other similar abilities.
- Superhuman Vocal Stamina: possesses superhuman stamina in his lungs, throat, and vocal cords.
- Sean was Catholic.