Johnny Depp understands his 'Alice in Wonderland' character's Madness.

The American actor - who plays the Mad Hatter in director Tim Burton's fantasy-adventure movie 'Alice in Wonderland' - said he was dragged into his characters odd sense of reality whilst researching Lewis Carroll's classic story.

The 46-year-old star said: "I started reading the books and understanding the character and the significance of the letter M. There's a moment when he says, 'I'm investigating things that begin with the letter M'. That was huge for me. Hatters were referred to as mad because of the mercury they used to use in the glue. Mercury was the M. I found that fascinating."

Johnny recently admitted he found the movie "exhausting" because he'd spent so much time filming against a green screen so CGI animated characters could be added later.

He said: "The green itself is exhausting. It beats you up. You're kind of befuddled at the end of the day."