Age: 57
Occupation: Supreme Court Chief Justice
Led by Roberts, the Supreme Court is examining some of the hottest buttons in U.S. law: affirmative action, immigration enforcement and, foremost, President Obama's health care reform. Anthony Kennedy has traditionally been the swing vote on an ideologically split bench, but a recent American Bar Association survey found that legal experts believe Roberts is more likely to break from the conservative bloc and uphold health reform. Either way, his role this year will be more momentous than ever.