There are a lot of superheroes out there, but Batman might have the greatest cache of villains. From Penguin (who's getting his own HBO Max series) and Riddler to Mr. Freeze and Bane, there are so many Batman baddies that have proved themselves worthy of main villain status. Yet, many of them get caught up as members of the Rogues Gallery because the Joker will always and forever be the Batman villain.
Since 1940, The Joker has been a Batman staple. There have been many different interpretations of the classic clown character. Some have been comical (like Mark Hamill's version); others have been relatable (like Joaquin Phoenix's version) and some have yet to be explored (like Barry Keoghan's version). Then, there was Heath Ledger's Joker -- grounded, joyless and captivating. Ledger's Joker was also notorious for not having an endgame. All he wanted to do was make the world burn. However, there's a fan theory circulating that posits the Joker as a hero.
How Batman Inspired the Joker In The Dark Knight Trilogy
Over the years, each version of the Joker had its own origin and motivations, but most of them did have some kind of backstory. Yet, The Dark Knight didn't include an origin story for Heath Ledger's Joker. To find that, viewers have to go back to Batman Begins, where the Joker's origins were briefly alluded to. At the end of the film, Gary Oldman's Commissioner Gordon brought up the topic of criminal escalation before pulling out a Joker card and giving it to Batman.
That brief exchange showed two important things about The Dark Knight universe. First, Gordon made it clear that Batman's masked vigilantism was only going to inspire more off-the-wall villains. While that was somewhat obvious, the Joker card made things interesting. While giving the card to Batman, Gordon implied the Joker was a new threat to Gotham, meaning that Batman's shenanigans had directly motivated or inspired the Joker. If that's the case, then Heath Ledger's Joker wasn't created by falling into a vat of acid; rather, he was simply someone who wanted to imitate Batman.
Could The Joker Be a Hero in The Dark Knight?
The idea of the Joker as a hero is where things really get going. According to an Unddit theory by Vast_Number_6761_, the Joker was actually trying to do the same thing as Batman. Thus, The Caped Crusader's success as a vigilante prompted the Joker to operate outside the law as well. There was a key difference, however. While Batman sought to strike fear into the hearts of criminals, the Joker wanted to scare innocent people into what would happen if they gave into their inner selves. As such, the Joker's true mission was to show how the true state of humanity was chaos and anarchy.
It's a great theory, and it casts the Joker in a new light. However, the whole thing falls apart in Christopher Nolan's universe. In The Dark Knight trilogy (which set the bar for dark superhero films), vigilantism is painted in a morally-gray light, so it's Batman's personal morals that make him a hero. Thus, when Joker starts blowing up hospitals and innocent people, the audience perceives a problem. Even though Batman and The Joker are showmen and vigilantes, they have totally different reasons for exiting. The Joker can never really be a hero (regardless of how many mobsters and gangsters he kills) because his morals are never about protecting the innocent.