It's everybody's favorite green-haired insane freak. It's The Joker.
I know you might hate me for saying this but, though I thoroughly enjoyed Heath Ledger's performance in The Dark Knight, I have to say that my favorite Joker is still Mark Hamill. Call me crazy but I think nostalgia plays a big part in that opinion.
Thank you Bruce Timm. You created my favorite iteration of the Batman.