The Batman: Deleted Arkham Scene

Although Barry Keoghan is simply credited as "Unseen Arkham Prisoner," it's obvious that he is the Joker. Director Matt Reeves has revealed that in The Batman's universe, Keoghan's Joker has had his scars from birth and his permanent smile is the result of a congenital disease, so he can't stop smiling. Batman has already encountered Joker in his first two years and they have a history together, although he isn't calling himself Joker yet. The obscured makeup was based on Conrad Veidt's appearance in The Man Who Laughs (1928). Veidt's role in this movie was the main influence for writers/creators Bill Finger, Bob Kane and Jerry Robinson to create Joker.

Edited from The Batman (2022)