Heath Ledger improvised half of his comedic dialogue on set.

According to Terry Gilliam, the last line Heath Ledger spoke for filming on the set was “Don’t shoot the messenger.” When Johnny Depp filmed his role after Ledger’s death, Depp asked Gilliam if he could try a new ad-lib: “Don’t shoot the messenger”, unaware that Ledger had improvised an identical line.

After the death of Heath Ledger, production was shut down for a few months. Then it was re-started when Johnny Depp, Jude Law and Colin Farrell agreed to complete Ledger’s role. The film’s fantasy premise, and some clever rewrites, let the actors play a man whose appearance changes as he travels between imaginary worlds.

Heath Ledger’s last movie project. It is dedicated to him along with William Vince.

The Joker’s face paint was reportedly designed by Heath Ledger himself, who used white clown makeup and cosmetics from a drugstore. Once his design was approved, the makeup team was responsible for replicating the look each day for filming.

During the chase scene, when the Joker takes over driving after his driver is killed, the bullet holes on the windshield form a smiley face.

Heath Ledger directed both homemade videos that the Joker sends to GCN himself. The first video involving the fake Batman was done under Nolan’s supervision. Nolan thought Ledger had done so well with that sequence, he felt there was no need for him to be there when it came time to film the scene where reporter Mike Engel reads the Joker’s statement. He put his trust in Ledger and let him do whatever he wanted, ultimately pleased with the result after he’d seen the outcome.

Christian Bale stated in an interview that during the interrogation scene, Heath Ledger wanted him to beat him as hard as he could to get the real feeling of what was required from the scene.