It's a long time since The Dark Knight took the world by storm and we still can't stop thinking about Heath Ledger's incredible performance as the Joker. Originally met with a fan backlash that makes Ben Affleck's Batman feel loved, as publicity stills and trailers were slowly released it became apparent that Ledger had delivered something incredibly special.
This is made all the more impressive as it was an accepted 'fact' amongst the fans that no one could ever do the character better than Jack Nicholson in Tim Burton's Batman. Now that sentiment feels laughable; next to The Dark Knight's version, Jack Napier could pass for a genuine children's entertainer.
One of the biggest elements of the character that Nolan's version trumped Burton's was in the origin, or lack thereof; unlike Nicholson, whose story provided the main arc, we learnt nothing about Ledger's origins. This is incredibly faithful to the source - throughout the majority of his appearances in the comics any backstory of the Joker has been kept vague or presented in a highly subjective manner - and helped make Joker an even more captivating screen presence.
But because we're gluttons for reading too much into things, that hasn't stopped us coming up with a few possibilities of where he came from.
Here are eight theories, using evidence from the films and other material, that try and crack the Joker's origins.