I've settled on the retired hit man. Meet Eric Stone.
High Concept: Retired Shadowy Killer of the Underworld
Eric Stone was one of the best assassins in the country. His name is a legend, and a byword for oncoming death. But he's been out of the trade for a couple years now.
Trouble: I Hate What I've Become
Stone has killed men, women, children and dogs. If it walks or crawls on the Earth, he's probably killed it. And it started to break him. The final straw was when he was hired to kill a prostitute to keep her from talking to the police about a high ranking mob boss. Unbeknownst to him the hooker was a White Court Vampire. Still, he couldn't do it, and vanished from the underworld, vowing he wouldn't take up a gun again.
Phase One, Where did you come from: Gun Fu Master
Stone grew up in the streets of Atlanta, a thug who found a gun and the means to make himself a name. He had killed several people in robberies before he was eighteen, and caught the eye of a hit man named Marco Windberg. Windberg took Stone on as an apprentice of sorts, and taught him how to be a contract killer. Stone's talent with firearms far exceeded Windberg's, and he soon broke away from him to make his own way.