The Nolan/Ledger Joker differed from many of his past iterations in the fact that rather than explicitly assigning him a backstory, or ignoring it altogether, they deliberately obscured his past. By having him tell different versions of the story of how he got his scars to different people, the audience is left not knowing which, if any, is real. The resulting effect is of a truly unnerving, yet fascinating character. Leaving the ‘gaps’ may have been necessary (for reasons of time or the flow of the film) but Nolan, like Bacon, paradoxically uses the void to enhance his work. The effect for the audience is the same as that which Bacon has on Nolan – they are left ‘thinking about what’s in that dark space behind’.
Interestingly, while Nolan developed the Bacon link, he was not the first to notice the connection. Tim Burton’s 1989 Batman film has the Joker intervening to save just one piece of art from destruction at a museum: Francis Bacon’s Figure With Meat.