AGE 20: Justin Bieber

Musician and model

What makes him powerful: It hasn't been an easy year for the Biebs. After run-ins with the law and the paparazzi, Bieber disappointmented a lot of fans. There was talk of deporting him back to Canada. Still, he remains the highest-paid celebrity under 30 and seems to be trying to reinvent himself, including becoming the new face of Calvin Klein and signing up to be "roasted" on Comedy Central in March.