Heath Ledger's Joker has, in the years since The Dark Knight, proved so good the Oscars had to restructure the Best Picture award and become an undisputed icon, an emblem of how superhero cinema can go so far beyond men in silly costumes stage fighting. The scrawled on make-up, the Tom Waits-inflected voice and all the subtle little tics you only pick up on when watching the film for the thirtieth time; it's a beautiful meeting of actor and material so completely realised it transcends the hype.
Of course, the now-definitive screen Clown Prince of Crime didn't just walk into Gotham fully formed. Ledger invested months in fully immersing himself in the character, starting before the Nolan brothers had even finished the script, shaping the character in as fundamental ways as the writers. Naturally that means quite a lot changed in the time between the first tease at the end of Batman Begins and mask removal at The Dark Knight, with an entirely different version of the character at points possible.
The origins of the character himself are purposely vague, but thanks to interviews with Christopher Nolan, David S. Goyer and the late man himself, a picture of where Joker the performance came from can be painted. And it's a crazy one.