Originally Posted by Happy Jack
Joker's one of the few villains I can think of that truly benefits from having an anti-backstory. He's such an over-the-top, theatrical character that it's always a bit hard to swallow that he was ever a relatively average mob enforcer/crook/comedian/whatever. When you remove all of that (or at least make it very vague) it liberates him in a sense, to be less of an identifiable man and more of an anarchic counterbalance. Plus it plants for firmly in opposition to Batman, who of course has a very detailed and rich origin.
Joker has a backstory, we simply don't know what it is. Today I saw a strange looking fellow in plaid pants walking down the street. I didn't know his name and I didn't ask him his name therefore I will probably never know his name. But that does not negate the fact that he still has
a name. The exact same thing goes for the Joker's origin. We don't officially know exactly what it is and we may never know but that doesn't negate the fact that he still has one.
And with that said, I like it best when we get to speculate about it. I quite like Rincewind's deductive reasoning. And I know that the logical thing is to think that he had a tough life but I have always loved the idea of 'one bad day.' That's my favorite take. As for TDK Joker, I imagine that he was always a bad or shady guy. A schemer of sort who got on the wrong side of the mob and they gave him the glasgow grin(and he seemed to hate the mob more than the cops). That or I imagine the scars were self inflicted- maybe he's a mad man who probably broke out of an asylum but was never identified and took the first train to Gotham. Joker definitely struck me as having already been in an asylum before.