Barack Obama topped Forbes's list of the world's most powerful people in 2011, as the US leader's clout rose after the deaths of al-Qaeda leader Osama bin Laden and Libyan dictator Muammar Gaddafi.
Obama bumped Chinese President Hu Jintao from the No. 1 spot on the magazine's annual rankings.
German Chancellor Angela Merkel remained the most powerful woman at No. 4 on the list, as Europe's largest economy continued to wield its influence over the troubled European Union.
Russian Prime Minister Vladimir Putin, who is running again for president, was No. 2 and Hu came third as he gradually manages the transition of power to others in China.
"The US remains, indisputably, the most powerful nation in the world, with the largest, most innovative economy and the deadliest military," Forbes wrote.
Obama's approval ratings have fallen at home as he struggles with stubbornly high unemployment and a tepid economy, but his fortunes on the world stage have been quite different.
Under orders from Obama, bin Laden, who helped orchestrate the September 11, 2001 attacks on the United States, was tracked down in Pakistan and killed in May after 10 years in hiding.
The United States joined the NATO-led intervention in Libya, which began with air strikes in March and led eventually to Gaddafi's death in October.
Microsoft co-founder Bill Gates at No. 5 was the first corporate executive on the list, thanks to a malaria vaccine backed by his charitable foundation that recently passed a key clinical trial.
"Gates' goal is to eliminate infectious disease as a major cause of death in his lifetime. He may succeed," Forbes wrote.
Mark Zuckerberg, the 27-year-old head of social networking site Facebook, shot into ninth position from No. 40 in last year's vote, sandwiched between US Federal Reserve Chairman Ben Bernanke (No. 8), who overseas monetary policy for the world's biggest economy, and British Prime Minister David Cameron at No. 10.
"What the CIA failed to do in 60 years, Zuck [Zuckerberg] has done in 7: knowing what 800 million people think, read and listen to," Forbes wrote.
The king of the world's largest oil producer Saudi Arabia, Abdullah bin Abdulaziz al Saud, came in at No. 6 and Pope Benedict XVI was No. 7.
For a full list of the world's most powerful people click here.