TheBatman director Matt Reeves explains Barry Keoghan's Joker look in The Batman deleted scene:
✖ Why so scarred? That's the question mark surrounding the Unseen Arkham Prisoner hidden in shadow, only to be revealed as a proto-Joker when he has the last laugh with the Riddler in the final moments of The Batman. Director Matt Reeves has since released a five-minute deleted scene showing the Dark Knight detective interrogating Joker to profile the Riddler, a serial killer hellbent on unmasking the truth about the corrupt Gotham City.
Reeves revealed the inspiration for his"Joker who's not yet the Joker": a homage to the mutilated mouth of Conrad Veidt's Gwynplaine in The Man Who Laughs, the 1928 silent film that influenced the DC Comics character. "He can never stop smiling. And it made Mike [Marino] and I think about — I was talking about The Elephant Man because I love David Lynch. And I was like, 'Well, maybe there's something here where it's not something where he fell in a vat of chemicals or it's not the [Christopher] Nolan thing where he has these scars and we don't know where they came from," Reeves explained.