He's played by Heath Ledger in the best live-action performance of his character ever. Then the actor died, making this his iconic last role and making the movie itself something you had to see out of respect for the guy... and because it looked pretty awesome to begin with.
Also, he is voiced by Mark Hamill (Luke Skywalker) in the animated series as well as in the two most recent video games (one not released yet). The fact that this voice will soon be retired (if not Mark Hamill retiring entirely) will probably be one of the saddest days for Batman fans as Mark did an amazing job with Joker's voice. The laugh as spot on and the variety in tone just worked. Whenever I see or hear another Joker animated series, I think of how it pales when this Joker is absent from the scene.
Lastly, he's probably the best villain of anything of all time. This crazy ************ just does what he does because he likes to see what sort of chaos it will bring. His trademark schemes are silly, but somewhat hysterical. And when he isn't trying to be funny, he'll deliver a good line or two that will get a good laugh out of me. Despite all that silliness he brings to the table, his madness twists him into one of the series' darkest characters and is probably what makes him so well liked amongst all the Batman villains.
So... yeah... That's why my avatar is awesome. Sorry for such a long post.
