He may not have any powers, but he's insanely intelligent and resourceful. Also he's a lot like the street level heores from Marvel (Luke Cage, Iron Fist, Daredevil, Spider-Man, etc.) when it comes to his job and the sorts of villains he deals with, but unlike them he's also dealt with much greater threats against the world as a whole and is technically one of the few men who can kill Superman. For that, he's a superhero.