Joaquin Phoenix says playing The Joker is "terrifying".
The 44-year-old actor admitted he had no real preconceptions going into the title role in Todd Phillips' upcoming DC Comics blockbuster tackling the origin of Batman's greatest villain, and the potential for danger is what sold him on the role.
He told the New York Times: "I didn't really know what it was. I didn't know how to classify it.
"I didn't say, 'This is the character I'm playing.' I didn't know what we were going to do. It was terrifying."
Phoenix explained his criteria for his roles is quite a simple one, in that the projects have to carry "a unique vision" above all else.
He added: "I don't really care about genre or budget size, anything like that. It's just whether there is a filmmaker that has a unique vision, has a voice, and the ability to make the film."
The 'Walk The Line' star revealed he always asks himself the same question when it comes to deciding whether or not to take on a new project, and he only sees his film career coming to an end when either he or the audience gets bored.
He said: "What's going to keep me excited or inspired, and wanting to work hard?
"If I don't feel like I'm pushing myself in some ways, I'll get bored, or maybe they'll get bored of me. I don't know who's going to get bored of who first."
Meanwhile, filmmaker Phillips recently admitted it was a challenge to convince Phoenix to star in the upcoming movie.
He said: "I was going to his house, basically begging him to do the movie. I go, 'So I keep coming up here every day. At some point you, you gotta say are you in or out.'
"And he said, 'That's not how you do it'... I always say he never really signed onto the movie. One day he just showed up at a wardrobe fitting."