Bradley Cooper says it was his idea to perm his character's hair in 'American Hustle'.

The 38-year-old hunk looks unrecognisable in his role as Richard DiMaso in the '70s crime caper, but the former Sexiest Man Alive admits it was his idea to sport the unappealing look to add another dimension to his character.

Quizzed if the perm was his idea or director David O. Russell's, Cooper said: ''My idea. And then he sort of took it, as he does, and made it an amazing aspect of the character.

''We were talking about making Richard DiMaso look different than I do, so I thought, why don't we perm his hair? He curls his own hair every day because he wants to look like these black baseball players like Dock Ellis and he thinks that's cool. I was like, 'Wow, OK', and it all just sort of happened.''

The film sees Cooper reunite with his 'Silver Linings Playbook' director, Russell, and co-star Jennifer Lawrence, and the actor reveals he didn't take much convincing to sign up.

He told Collider.com: ''He [Russell] didn't pick up the phone because I was sitting right next to him because we were editing 'Silver Linings Playbook'. I was there watching him as he was cultivating this whole idea, and the notion, and the script, and reworking it and creating these characters. I had a front row seat [as he developed the movie].''