Joker writer and director Todd Phillips has said that his version of the clown prince of crime does not follow any established elements from the DC comics, and that Joaquin Phoenix’s character is a unique, original interpretation.
Talking to Empire magazine, Phillips said “We didn’t follow anything from the comic-books, which people are gonna be mad about. We just wrote our own version of where a guy like Joker might come from. That’s what was interesting to me. We’re not even doing Joker, but the story of becoming Joker. It’s about this man.”
It was clear from the first trailer for Joker that this was going to be a very different kind of super villain film, with its Scorsese vibe and heavy political tones. But Phillip’s words mean you can discount any story threads from The Killing Joke finding its way into this R-rated film.
Source: IGN.com Joker 'Doesn't Follow Anything From the Comics'