Matteo Renzi, 39
The youngest prime minister in Italian history came into office in February on a burst of promise. A charismatic outsider, he pledged to break his center-left Democratic Party’s long ties to labor while he chased renewal by challenging Europe’s zeal for austerity. He’s auctioned off state-owned luxury cars and sacked the chiefs of state-owned companies, shaking up the country’s entrenched ruling class. But his more sweeping aims have collided with reality. His political and economic reform agenda is now meeting stiff resistance in the Italian parliament. And it may be sunk by a more urgent concern: the country is suffering a triple-dip recession that’s wiped out all its growth since 2000, complicated by a crushing debt load. In the face of all that, Renzi is vowing to press ahead, marshaling the optimism that swept him to power.