It can be said without any argument that Batman is as identifiable as The Joker, purely on the basis of that they're almost always seen together.
We know Batman from the cowl, the cape, the grim look on his face and how he's in complete contrast to The Joker. This isn't even for a comic-book fan or a movie fan, either. You could stop anyone walking down the street and they'd be able to point out an outline of Batman with little or no prompting. Same goes for The Joker, too. You see the white face, the red lips, the green hair and hear a maniacal laugh and you think of either Jack Nicholson, Cesar Romero or Heath Ledger.
So, what next identifies Batman? His origin story, of course. We know that Batman is an orphan, that his parents were brutally murdered in front of him and that this inspired him to become Batman. Again, this story is almost as familiar as the suit. But what about The Joker's origin story? Again, this part of it gets trick for the average punter on the street. Some might fuzzily recall Jack Nicholson being dropped into a vat of acid by Michael Keaton, others might recall Heath Ledger telling different stories of how he procured his scars, and others - definitely the more faithful - will either point to Alan Moore's 1988 comic The Killing Joke, and argue that that's the definitive origin story for The Joker.
The fact is, of course, is none of them really matter. What's always been at the centre of the Joker is not who the character is, but what's he up to. Realistically, it doesn't matter if the Joker got his scars from a loan shark, or if he fell into a vat of acid, or if he self-mutilated - what always drove The Joker was what he was going to do. There was never any reason to explore it either, primarily because the mystery of his origins was all the more thrilling. After all, who in their right mind would dress up in purple, cover themselves in clown makeup and use helium balloons to dispense nerve gas on a city? Whilst blaring out Prince and cackling while he was doing it?
Every iteration of Joker worked on theatricality. Even Heath Ledger's version used sweeping, broad methods to make a point; why he was doing it in the first place and what started this all off for him was never explored - because it wasn't necessary and nobody cared. Moreover, trying to ground him in reality or giving him a logical explanation for the way he was and how he acted was in direct contravention to what he stood for. He's the Clown Prince of Crime, the Jester of Genocide, the Ace of Knaves, the Harlequin of Hate, he's not some guy with a real name or a story. He's The Joker.
In an interview on the Joe Rogan Experience this week, Brendan Schaub discussed the Joker origins film and gave a snifter of what's in store for the film. Schaub's connection to the film is through Todd Feldman, an agent at CAA who represents both Schaub and Todd Phillips. According to Schaub, the film will "dark. It’s like a dark Joker. As a kid, he had a permanent smile and everyone made fun of him. It’s like on the streets of Brooklyn. It’s super dark and real." Earlier this week, Deadline's report described the film as "a gritty and grounded hard-boiled crime film set in early-’80s Gotham City that isn’t meant to feel like a DC movie as much as one of Scorsese’s films from that era, like Taxi Driver, Raging Bull or The King Of Comedy."
While it's true, most comic-book movies work best when they're within a specific genre, the fact remains that The Joker simply isn't supposed to have an origins story. In a 2008 interview with Wired, Nolan summed up The Joker as "like the shark in Jaws... The Joker cuts through the film, he’s incredibly important, but he’s not a guy with a backstory. He’s a wild card." While it's true, there's fertile ground to build up a film around The Joker, and he's as recognisable as any comic-book villain you can think of, it still doesn't change the fact that what made The Joker so effective was that we never knew where he came from.
It should be kept that way.