The Joker did it to himself IMHO. I'm not going to tell anyone they are wrong. It's a movie. But..

When you look at The Joker.. Or Batman.. or really most of the character's in Nolan's Batfilms they have one thing in common.. Bad upbrings.

When you see Batman you think.. man wtf happened to him to make him want to do this shit? You want something to be able to point to and say ok that is where he lost his shit. Of course watching his parents get blown away will do things to you.

But with The Joker.. it's just bullshit. A different story for each victim. He gets off on it. I'm sure his childhood was terrible. There is no telling.

There was no defining moment that made him. And he more then likley gave himself the scars just for the hell of it. To play with people. The man is truly sick. He prays on mentally ill people. Yeah I'm pretty sure he gave them to himself.