Tommy is a hitman, it's not a good living but it pays the bills. Since being bitten by an alien and awakening with super powers he's made a living from...well killing people with super powers.
Tommy doesn't do good guy's it's a rule he has. He also doesn't drive but that's because he doesn't know how. His attempt to get into The JLA was motivated by a single desire, to check out Wonder Woman with his X-Ray vision. Tommy is a hitman with style and a bad relationship with demons. He also has a sense of honour, even if it isn't obvious.
A gun, several guns in fact but that's beside the point.
Hitman has X-Ray vision, just like Superman's, and has telepathy, not like Superman. Other than that he is an adept gunman and is good at staying alive.
It's not Kryptonite, that's for damn sure, a person would best do to enter into a combat situation with him using a telepathic scrambler. His X-Ray vision would stop any chance of a sneak attack but you could keep him from knowing your moves and get inside his effective range before taking him out.