I think he was simply a small time criminal who fell out with the mob at some point, which would explain his disdain for them and all their petty trappings like money and status. Either criminals, or he himself, are to blame for the scars, and after hearing of the "theatrical" Batman, he took it upon himself to design a "look" and start knocking off the mob banks.
The more interesting aspect of his origin I think is where exactly does his philosophy on human nature come from? He seems to me, like someone who was betrayed at some point by another's dishonesty. Somewhere along the way he appears to have lost faith in human beings ability for good, and in order for that to happen, he had to have that faith to begin with IMO. Something happened, perhaps the event that eventually scarred him, where he felt betrayed and taken advantage of by his faith in good people, or someone being "a man of their word." The Greatwun suggested a military past, and to me, that makes alot of sense potentially, war brings out the worst in people and you see up close and personal how terrible we can be. It's also an environment where you have to depend on the word of the next man, that they have your back. Some kind of incident in a situation like that can change your perception of human beings pretty fast. His life's mission is to prove that noone is beyond corruption and evil, and that has to come from some kind of trauma he experienced in his life
