Banshee

Factor Three got to Sean Cassidy first. They found a widowed Interpol officer with a family castle in Ireland, fitted him with an explosive control collar and pointed him at the X-Men, which means Banshee entered the series as a villain and fought his way out of it. That makes him one of the only Silver Age antagonists Marvel promoted straight into the hero column rather than redeeming over decades. His scream is not a shout, either. It is a precisely modulated sonic beam that shatters steel, and by riding his own pressure wave he flies.

What makes Banshee matter is age. He joined the Giant-Size team as the adult in the room, old enough to have a grown daughter, a career behind him and a mortgage's worth of regret, and he became the team's conscience while Cyclops was still learning to lead. He blew out his vocal cords stopping Moses Magnum from cracking Japan open and spent years powerless. He loved Moira MacTaggert, ran Generation X's school beside Emma Frost, and founded X-Corps as an armed mutant police force that collapsed underneath him. Then a passenger jet and a brand-new Summers brother ended him.

Roy Thomas and Werner Roth built Banshee as a one-off Factor Three heavy, and Len Wein and Dave Cockrum rescued him for the 1975 relaunch as the international team's Irish veteran. Claremont used him as emotional counterweight for a decade and then took his voice away, a rare thing to do to a character defined entirely by it. The 1990s handed him the best job of his life as Generation X's headmaster. The 2000s handed him X-Corps, a betrayal and a knife across the throat, and Deadly Genesis killed him outright so Vulcan's debut would carry real weight. His daughter Theresa has since carried both of his codenames.