He is a stocky man in his early fifties with a bent nose and a prominent scar that ran across his face. He is also missing the little finger from one hand, lost because he angered the Imp.
He could've lost all his other fingers, but traded each finger for a favor owed to the Imp, giving her nine favors.
Her fingercutting was to show her as a person not to be messed with. As she summarized the situation:
You sold me out in exchange for the promise that Hexagon would kill the guy who hurt you. That’s just plain old revenge, which is about as personal as you can get. Now, what I did back, that was just business. After all, if word got out that I let you get away with selling me out like that, it would ruin my rep.