Hammerhead used to be a soldier for the mob... dumb muscle, a leg breaker. But then he survived a near-fatal head injury. He had most of his skull replaced with metal, and the rest of his body augmented with cybernetics. I've seen him run head-first into a brick wall and smash it to pieces. Wrap a machine gun into a pretzel. He's also hard-headed in the sense that he's stubborn... and that's how we'll get him.
References
Hammerhead is referenced in two of Detective J. DeWolff's audio journal entries (Jean DeWolff's Journal Part 02 & 03), in The Amazing Spider-Man 2 (videogame).
Bio
Hammerhead was originally the surname of this mob boss and then taken on as his street name after suffering a head injury where he had to have an operation on his head operation where missing parts of his skull were replaced with metal giving his head a strange shape. He acts and dresses like a 1920's gangster.