Heath Ledger ("Brokeback Mountain") has been cast as the Joker in "The Dark Knight," the sixth installment in the "Batman" series.

Variety reports Christian Bale is returning as the Caped Crusader, and Christopher Nolan is back in the director's chair.

"I'm excited to continue the story we started with 'Batman Begins,'" director Christopher Nolan said in a statement.

"Our challenge in casting the Joker was to find an actor who is not just extraordinarily talented but fearless. Watching Heath Ledger's interpretation of this iconic character taking on Christian Bale's Batman is going to be incredible."

The script for the film will be written by Nolan's brother Jonathan.

Production is scheduled to begin early next year, with a possible summer 2008 release date.