Hayden Panettiere

Some Heroes fans are still debating the meaning of "Save the cheerleader, save the world," but the catchphrase has definitely turned Hayden Panettiere into the sci-fi drama's breakout star. Her portrayal of the self-healing, indestructible Claire Bennet landed her on PEOPLE's Most Beautiful, FHM's Sexiest Women and Forbes' Celebrity Power 100 all before her 18th birthday.

Acting since she made a Playskool commercial at 11 months, Panettiere has starred alongside Denzel Washington (Remember the Titans), Kate Hudson (Raising Helen) and Julia Roberts (Fireflies in the Garden). In 2007, the young starlet made headlines when she began dating her much older Heroes costar Milo Ventimiglia for more than a year.