Banshee

Sean Cassidy is not a fan of the IRA and is willing to to brawl over Irish Republican Party members making deals in New York City, he's that opposed to a war of differences in his home country.

Banshee is a mentor to those willing to listen to stories about Irish myths and whatnot.

Background
Sean has been many things in his life- cop, coerced criminal, an X-Man, a teacher, a supposed member of the IRA and widower. For the early years of their lives, Sean and Tom Cassidy were like brothers, and they found at an early age that not only were they both mutants, but they were immune to each others' powers. The two remained close as they grew up, even when Sean went into law enforcement, eventually secretly becoming an undercover Interpol agent. Only one thing came between them; a stunning blonde with a penchant for motorcycles by the name of Maeve Rourke. Sean met Maeve when she rescued him from two corrupt police officers who were intent on framing the young man as an IRA scout (he was simply hitchhiking home from a concert). Despite having just met the girl, Sean used his powers openly in front of her. To his surprise, she wasn't the least bit frightened by them. He brought her home to Cassidy Keep, where Tom met her and was as smitten with her as Sean was. Sean was convinced that she would opt for Thomas over him- Tom was the charming heir to the Keep, while Sean saw himself as the bumpkin of the family. The two competed for Maeve's affection for some time, until she finally chose Sean over his cousin. Tom relented, only wanting to see the woman he loved happy, and even served as the best man at their wedding. The cousins remained civil, though they were far from being as close as they had been before. Shortly after their wedding, Sean had to go deep undercover for Interpol, unable to have any contact outside of the mission. Unbeknownst to him, Maeve was pregnant with their daughter, Theresa. She gave birth to the little girl while Sean was still incommunicado, and the news that he was a father was unable to reach him. Sean was, in fact, so deep undercover that not even the news of Maeve's death could reach him until he came home. She had been visiting family in Belfast when an IRA bombing had taken place, killing her. It was assumed by most that little Theresa had perished as well, the only person who knew she had survived was Tom, who had rescued the infant in the aftermath of the explosion. Tom wanted to surprise Sean with the news of Theresa's birth after he told him of Maeve's death to lighten the blow. Unfortunately, Sean was so stricken with grief, guilt and anger over his wife's death that he turned against Tom, collapsing the ground under his cousin's feet using his powers. Tom's leg was broken so badly in the fall that he would have to walk with a cane for the rest of his life. Tom became bitter over his cousin's actions, and decided not to tell Sean of Theresa's existence at all. He told Theresa that she was an orphan, and raised the young girl on his own. Sean threw himself into his work with Interpol, opting not to return to Cassidy Keep due to the memories it held. He worked for Interpol (and for a good while, the NYPD as a liaison) for 18 years until he was forced to quit after a botched mission in which the mercenary known as Deadpool killed the mobster they were trying to find information on (though in doing this, he saved Sean's life, as the criminal was about to shoot.). With all of this turmoil in his life, Sean fell into a deep depression. What was his point for living? No job to bury himself in. No family to distract him and love him for who he really was and not pretending to be...Nothing... After a night of drinking at a local pub(Irish of course), Sean began his lonely trek home only to be approached by a man. This man came from the shadows and spoke with a clarity that Sean had never heard before. He said his name was Charles Xavier and he said had a plan... Arriving at Xavier's Sean suddenly had a purpose, he had a meaningful existence again as not only a member of the X-men but as a teacher of music and life.

Personality
Sean Cassidy is a decent guy in the most simple ways. He's pretty laid-back, he's moral without being overbearing. He's what would be called a gentleman in times long gone. He does what he thinks to be 'the right thing.' That said, Sean draws a distinction between morality and legality. He'll occasionally break a 'petty law' in the interest of having fun, provided he's absolutely certain that no one will get hurt in the process. Overall, though, Sean does have respect for the rules. After all, he was a law enforcement officer for a good piece of his life before arriving at Xavier's mansion. In this though, he tends to focus on the spirit of the law rather than the letter, but Sean is still definitely a lover of rules. He thinks they help keep order. Yes, he's one of those.