A psychopathic supervillain Leto described his role as "nearly Shakespearean" and a "beautiful disaster of a character"; about portraying the villain, he stated, "I took a pretty deep dive. But this was a unique opportunity and I couldn't imagine doing it another way. It was fun, playing these psychological games. But at the same time it was very painful." Leto never broke character throughout filming, with Smith going as far as stating he never met him.

Ledger moves the Joker away from Jack Nicholson's interpretation into darker territory, and expresses his support for any potential campaign to have Ledger nominated for an Academy Award

A darker version of the Joker played by Jack Nicholson made his film debut in 1989's Batman, which earned over $400 million at the worldwide box office. The role was a defining performance in Nicholson's career and was considered to overshadow Batman's, with film critic Roger Ebert saying that the audience must sometimes remind themselves not to root for the Joker.