I find it interesting (no insult intended) that this version of the Joker has resonated with you and so many other people? When I was watching it the idea that I'd never see Heath Ledger reprise the role never entered my mind as it did yours. But due to your post I started thinking more and more about the psychosis of the Joker.

1. Horribly scarred physically and mentally. You don't now how or where cause he's constantly changing the story of how he got that way.

2. Much like Anton Chigur in "No Country for Old Men" he wants the everyday citizen to "get in the game" so he sets up situations where John and Jane Q. Public are forced to break the ultimated commandment and kill. Kill for survival, kill to protect loved ones or kill for vengeance.

3. His duel with Batman is the only thing that gives his life purpose cause in Bats he's found his mirror image almost as screwed up as himself. And much like "The Green Goblin" he want's the hero to abandon principals and morals and join the fun?

I susptect there'll be many a thesis written on this character.

Da Worfster