One of the most note-worthy transformations was Charlize Theron's portrayal of serial killer and former prostitute Aileen Wuornos in 'Monster,' which won her an Oscar for Best Actress. Prior to this role, Theron was athletic and had to put on weight, on top of masking her face with makeup and prosthetic teeth.

"I think I've tried most of my career to transform myself into characters. This was just more extreme," she's previously stated about the role. "I had about three months to gain weight. We never discussed it like, 'I'm gonna put on 30 pounds,' because I wasn't trying to look fat. It wasn't that hard. I just didn't say 'no' to Krispy Kreme doughnuts or anything that was full of cream. I also gave up exercising."

The above photo on the left shows Theron in 2003 ('Monster' premiered the same year) promoting the film on 'The Tonight Show.'

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