Warner Bros. initially wanted to give Heath Ledger's Joker an origin story in The Dark Knight. The second film of Christopher Nolan's Batman trilogy was the highest-grossing film of 2008 and received widespread critical acclaim, particularly for Ledger's dark portrayal of the Joker.
The Dark Knight saw Christian Bale return as the vigilante superhero who must protect Gotham City from the menacing and chaotic Joker. The Joker was introduced in The Dark Knight without a definitive explanation for where he came from or who he was before becoming the Clown Prince of Crime. Unlike Joaquin Phoenix' version of the character in director Todd Philips's award-winning 2019 film Joker, Ledger's Joker kept his origin a mystery, sprinkling different theories throughout the film of how he got the scars on his face. The only information the character ever gave up about himself was that his actions were purely driven by chaos. Ledger's performance as the Clown Prince of Crime earned him a posthumous Academy Award for Best Supporting Actor among several other awards. The character's mysterious aura was a major factor in why he was so intriguing to people. However, he almost did have an origin story.
During a Comic-Con@Home interview, The Dark Knight co-writer David S. Goyer revealed that Warner Bros. initially pushed for Joker to have an origin story. Goyer spoke about the elaborate villain origin stories usually seen in superhero movies and how they chose to go a different direction for the Joker. "I do remember when we were talking about, 'Well, what if the Joker doesn't really have an origin story?" said Goyer. "Even after the success of Batman Begins, that was considered a very controversial thing, and we got a lot of push-back. People were worried."
Throughout all the different adaptations of the Joker, the character's origins have never perfectly lined up. In the 1988 Batman: The Killing Joke comic, the Joker was a failed stand-up comedian who became a criminal to support his pregnant wife. In Tim Burton's 1989 movie Batman, he was a gangster named Jack Napier, who was behind the murder of Bruce Wayne's parents, and it's during a fight with Batman that causes him to land in a vat of acid. In Philips' Joker, he is a bullied and down-on-his-luck clown who dreams of becoming a successful comedian, but slowly descends into madness and eventually transforms into the villain.
Considering every Joker seems to have a different story in almost every adaptation, it seems fitting that The Dark Knight writers kept the origin story vague. While it would have been interesting to see what background Ledger's Joker would have had (to provide a sense of insight into who he was), not knowing makes the movie and character that much more unsettling. Perhaps the true reason he "got these scars" would have been revealed, but it's refreshing to have a villain who will forever remain a mystery.
Source: Comic-Con@Home2020