Simple solution: gorilla-like creature that can assume the form of a very hairy and ape-like human trying to fit into the human world and fights other monsters over a dick-waving instinct of "I'm the alpha male here".

Alternative solution: very hairy and ape-like human that can transform into a gorilla demon thing. He used to be a standard, rather hairless salaryman.

Extra solution: a very hairy and ape-like human who happens to possess the powers of the previous solutions without having a straight gorilla form.