1. Barack Obama

Title: President of the US

Country: US

Age: 54

President Barack Obama presides over the world's most influential country, giving him unparalleled responsibility and power. He's caretaker of the largest economy, and he's helped nurse it back to health since the financial crisis. Since taking office in early 2009 — amid a full-blown recession — the US has grown its GDP by $3 trillion, to $17.4 trillion, and in October unemployment hit 5%, the lowest mark since 2008. His legacy-making overhaul of the health-care system has helped trim the uninsured rate by a third, and it has now survived multiple Supreme Court challenges.

Obama's international track record is mixed. As commander-in-chief of the world's largest military — more than 2 million active and reserve forces and a defense budget of $560 billion — he's taken heat for failing to deal adequately with the growing turbulence in the Middle East, highlighted by the bloody Syrian civil war, the rise of ISIS, and the Taliban's growing strength in Afghanistan. Relations with longtime ally Israel have grown icy. Yet his sway in foreign affairs is still strong, as evidenced by his historic move to warm ties with Cuba and the momentous nuclear deal he brokered with Iran.

He may have just a year left in office, but Obama isn't sitting idle: In November he flexed his power again, killing off the controversial Keystone XL pipeline proposal once and for all, arguing it would have harmed the environment without improving US energy security.