Christopher Nolan kept this intact for Heath Ledger’s version of The Joker in The Dark Knight, but comedian and famous geek Patton Oswalt has an in-depth theory speculating that before he came to Gotham City to spread chaos, the criminal mastermind was a military intelligence operative specializing in interrogation.
The Joker is arguably the most famous comic book villain of all time, primarily serving as Batman’s arch-nemesis, but also causing trouble for many other heroes in the DC Comics universe.
Other than his psychopathic mirthfulness and love of purple suits, one of the things that distinguishes the Clown Prince of Crime from many other baddies is how most of his pre-white skinned, green-haired life is shrouded in mystery.