Age: 49
Occupation: President of the United States
Previous TIME 100 appearances: 5
It's during times of crisis, not calm, when a President's influence peaks. In 2011, a tepid economic recovery threatens the vitality of the nation as well as President Obama's prospects for re-election. A seemingly intractable budget fight in Congress could derail his legislative agenda. The Arab Spring has dramatically realigned the Middle East, and with it, U.S. foreign policy. And the fog of war now a decade old in Afghanistan and just beginning to gather over Libya clouds Obama's hopes for a peacetime presidency. There are few things more important this year than Barack Obama's leadership, or the limitations thereof.