She may have just blown it off the hinges. In “Monster,” Theron plays Aileen Wuornos, the highway prostitute who became America’s first female serial killer. Convicted of murdering six of her johns, Wuornos was executed in Florida 15 months ago. The movie, written and directed by first-time filmmaker Patty Jenkins, seeks to explain how this victimized woman became a villain, and places a love story between Wuornos and a conflicted young woman (Christina Ricci) at its center. “Monster” as a whole has been written off as mediocre, and criticized for being lurid and too eager to forgive Wuornos her crimes. Maybe so. But Theron, 28, has delivered a voracious, gasp-inducing performance that is almost certain to earn her an Academy Award nomination–and could even get her to the podium on Oscar night. “I was terrified that I wouldn’t be able to find an actress with the b-lls to do what was necessary,” Jenkins says. She found one. “As much as I thought Charlize could do it, I never knew how good she was going to be. There were days when I would be behind the monitor just freaking out,” she says. “I couldn’t believe what was happening.”

Neither could anyone else. After getting her break opposite Keanu Reeves in “The Devil’s Advocate” in 1997, the South African native seemed poised for leading-lady status. Instead, she ended up playing “the girl” in movies such as “The Cider House Rules” and “The Legend of Bagger Vance.” Since 2000 she’s starred in 10 films. Until last summer’s “The Italian Job,” almost all of them were box-office failures, including the sickly “Sweet November,” opposite Reeves, and the thriller “Trapped,” where she met her boyfriend, actor Stuart Townsend. Along the way, two projects that might have changed the tide crashed over her. She was scratched from “Chicago” in favor of Catherine Zeta-Jones, and, after developing “Sweet Home Alabama,” Theron walked away when she and the director couldn’t agree on which sort of movie to make. It went on to gross $127 million, and although Theron has no regrets, she knew it was time to rethink her career. “I was very close to getting bored.”

Jenkins, meanwhile, was trying to cast “Monster.” Wuornos was deeply damaged, both emotionally and physically. The role required shooting a brutal rape, lesbian love scenes, multiple murders and a dramatic (and unflattering) physical transformation. In other words, it had “Oscar” written all over it, and Jenkins got flooded with interest from actresses. Theron was not among them. “I went after her,” Jenkins says. “She couldn’t understand why I wanted her, other than maybe I wanted to make a hot lesbian movie.” During their first meeting, as Jenkins explained her intentions, “Charlize stared at the floor the whole time. She was incredibly somber.”

Although Jenkins didn’t know it, Theron had, at the age of 15, reportedly watched her mother shoot and kill her abusive father in self-defense. No charges were brought, and the actress and her mother remain very close. Theron has consistently declined to discuss the incident, but two days after their meeting, Jenkins got the yes she was hoping for: “She said she’d had to really absorb where she was going to have to go. To do this she was going to have to go to this incredibly dark, dark place.”

Theron packed on 30 pounds for the role, shaved off her eyebrows and wore snarled prosthetic teeth. Brown contacts covered her blue eyes; makeup turned her pale skin into a sun-damaged disaster. As shocking as the results are, it’s Theron’s raw, emotional hunger that gives the performance its power. “I wish more than anything that people could see this movie and not think about my looks,” Theron says. “But I know that’s impossible. The ‘beauty’ thing is just…”

Yes, the beauty thing. The conventional wisdom is that Academy voters love it when stars make themselves unattractive (sidebar), because it proves an actor is “brave” enough to eschew vanity. But maybe it’s that without beauty as a distraction, the audience finally sees the talent. “Some actors are comfortable just being themselves,” says Theron. “Julia Roberts rarely changes herself, and that’s great. She can get away with it and people don’t get bored. But I love actors who transform–Robert De Niro, Frances McDormand–and I feel like I’m one of those actors.” She pauses. “This movie has given me a new belief that I can wait for outrageously great parts. You can’t make a movie like this and go back. That would be torture.” She laughs. “I’d rather just quit the business.” That’d be a shame. Charlize Theron is finally getting started.