For her Oscar-winning role as Aileen Wuornos in Monster, Theron gained 30 pounds and wore prosthetic teeth to portray the real-life serial killer. And in her latest film, Mad Max: Fury Road, the 39-year-old actress shaved her head.
The looks are shockingly different—and a far cry from the more glamorous roles, such as Queen Ravenna in Snow White and the Huntsman -- but Theron says it's all about respect.
"Every movie is its own animal and you have to respect it and treat it that way," she tells ET at the premiere of her new film. "This one was just a naturally a long process because the movie took so long to make, but I had a lot to have the story really inform me as to what I needed to do and what needed to happen. So I was grateful for the time."
In fact, shaving her head was not only for the role but a necessity for making Mad Max.
"I just had this moment where I was like, 'I need to shave my head! I can't think about what I'm going to do with my hair in this movie. I'm going to be in the desert. I'm a new mother. Let's just shave it,’” she revealed to ET in April. "The next day we did it. I can't even imagine doing it any other way."
And speaking of becoming a mother, Theron tells ET what she has planned for Mother's Day.
"The whole family is trekking down to Cannes," she says. Of course, that includes her mother, Sean Penn and her son Jackson, who she has to make it up for not taking him to the premiere.
"He was a little upset that he wasn't invited to the party tonight," Theron says.