Best known as Star Wars' Luke Skywalker, Hamill will lend his voice to perennial villain The Joker, while Conroy will be voicing the dark knight himself. Both are reprising roles they've filled in numerous other animated Batman projects.
Developed by Urban Chaos: Riot Response veteran Rocksteady Games, the third-person action-detective game will arrive on PC, PS3 and Xbox 360 next summer.
Mark Hamill has done the voice of Joker before. Taken from Wikipedia:
"He voiced the Joker in a few Batman-themed video games, notably Batman Vengeance and the Sega CD version of The Adventures of Batman & Robin."
Yup, he's done the voice of The Joker in a lot of different projects, as I noted in the story.
He also did it for "Batman: The Animated Series".