At just 18, British-born beauty Mischa Barton has taken over prime time in Fox's deliciously over-the-top ensemble drama, The O.C. As Marissa Cooper, the privileged and complicated sexpot whose youthful angst plays out amid a haze of drugs and alcohol, she breathes life into a character recognizable from any high school: the one boys love and girls secretly hate. No Juliet or Guinevere, Marissa is a petulant modern-day heroine worthy of Orange County, home turf of the late John Wayne, the California G.O.P., and countless rich white suburban teenagers.

Barton grew up in Manhattan and has been acting since she was eight years old. She landed the lead in a New York stage production of Tony Kushner's Slavs! at age 9 and a Calvin Klein campaign at 11, followed by more theater and a few independent films (Lawn Dogs, Lost and Delirious). In 2002, The O.C.'s executive producer McG (who directed Charlie's Angels) "discovered" her. "He just fell in love with me, I guess," says Barton. "At least that's how he says it."

With the show now in its second season, Barton expects her character to continue evolving, but she's got a firm grasp on the basics: "I am a rich, snobby girl who is wise beyond her years yet caught up in the popularity system." Already a Neutrogena spokeswoman and a fashion "It girl" with an equally gorgeous boyfriend, Brandon Davis—who just happens to be the grandson of the late billionaire movie mogul Marvin Davis—Barton has had such success with the real-life popularity system that some fans have begun to suspect her, however unfairly, of Marissa-like qualities: "So many people think I am my character—the snobby alcoholic. Television has a lot of power these days." But while there's little danger of Barton's becoming her generation's Shannen Doherty, a little art-house moonlighting might help soften her edge. "I'm going back to film," Barton says. "I could be doing an independent in the next two weeks."