By Jason Lynch
February 23, 2004 12:00 PM

Playing a serial killer is not exactly a part actors want to bring home with them. So Charlize Theron—who had gained weight, plucked out her eyebrows and donned fake teeth to portray Aileen Wuornos in Monster—took additional drastic measures to decompress after filming last winter. Each night the actress would flip on “mindless television” like elimiDATE and The Bachelorette. “I could sit on the couch and there was no thought process,” says Theron. “It was a whole new discovery for me.”

Monster is providing audiences with their own discovery: Theron can do a lot more than spiff up a red carpet. Her portrayal of Wuornos—a Florida prostitute who was executed in 2002 for killing at least seven men—”is one of the greatest performances in the history of cinema,” raved Roger Ebert. With her win at the Golden Globes, Theron, 28, is a front-runner for a Best Actress Oscar. After years of playing gorgeous-girlfriend parts in films like 2000’s Reindeer Games, “she’s showing everybody,” says Italian Job costar Seth Green, “that she’s capable of doing what any of the great actors have accomplished.”

In true Robert De Niro fashion the 5’9″ Theron put on 30 lbs. in three months with the help of potato chips, Krispy Kreme doughnuts and “creamy, cheesy stuff,” she says. But her transformation was more than skin-deep. “I had to get my body to the place of a woman who’d been living a homeless life since she was 14,” she notes. “Once I tapped into the emotional side of how she led her life, the physical stuff just happened naturally. All that tension she carries in her jaw and her mouth and her eyes—she reminded me of a stray dog who’d been kicked so many times that if you reached out a hand of love, she’d still recoil because she’d been betrayed so much.”

It’s the kind of beauty-plays-beast turn that makes Oscar voters swoon—unless they’re jealous of how quickly she snapped back to her stunning self. “It took seven weeks,” says Theron, who had to banish the paunch in time to start shooting the romantic drama Head in the Clouds. “Your best friend becomes the treadmill.” Luckily she had boyfriend Stuart Townsend, 31, to lean on. The couple fell in love while filming the 2002 kidnapping drama Trapped and costar again in Clouds. “They’re in sync. He’s just a caring, down-to-earth guy,” says Trapped producer Mimi Polk Gitlin, who introduced the pair. As for rumors they’re engaged, “we’re not getting married,” Theron told Britain’s Daily Telegraph last week. “I’m not opposed to marriage, but my life has been the kind of journey in which whatever happens happens.”

It hasn’t been the easiest of journeys. In 1991, growing up on her family farm in Benoni, South Africa, Theron, then 15, watched her mother, Gerda, shoot and kill her alcoholic father, Charles, a French road-construction company owner. Authorities ruled the shooting self-defense. “I wish I can change it, I can’t,” Theron told Diane Sawyer last month. “And I know that if my daughter was in the same situation, I would do the same thing.” Today the murder is “a part of me, but it doesn’t rule my life.” Says Monster costar Bruce Dern: “She’s not a wounded bird by any means.”

At 19, Theron moved to L.A. to try acting, honing her English (her first language is Afrikaans) by watching Nickelodeon and reruns of The Love Boat. When she auditioned for 1996’s That Thing You Do!, says producer Gary Goetzman, “I’ll never forget Howard Feuer, our casting director, screaming down the hall, ‘I’ve got a young Kim Novak in the room!’ ” Breakthrough roles in 1996’s 2 Days in the Valley and 1997’s The Devil’s Advocate put her on the map, but ultimately, says Shane Paish, Theron’s frequent makeup artist, “she wanted to do something” more interesting than standing around being a pretty girl.”

Thanks to Monster, Theron hopes those roles are gone for good. “You can’t make a movie like this and go back,” she told Newsweek. “I’d rather just quit the business.” Not to worry, says Trapped producer Gitlin: “After this, there’s no stopping Charlize. There’s nothing she can’t take on.”

Jason Lynch. Tom Cunneff, Dana Meltzer, William Keck and Amy Longsdorf in Los Angeles