34. Rex Tillerson

Title: CEO, Exxon Mobil

Country: US

Age: 63

Rex Tillerson runs the world's largest publicly traded oil company, commanding about 75,000 employees and generating nearly $400 billion in annual sales. But the oil industry can be a beast of its own, regardless of a company's size.

After a joint venture in the Arctic Sea between Exxon Mobil and the Russian firm Rosneft went up in smoke because of sanctions against Russia, Tillerson said in March that Exxon had been compensating by cutting costs and ramping up production in US shale fields. The company also came under investigation in November after reports suggested the company had for decades lied to the public about climate-change data.

The lifelong Texan and Exxon employee will reach the company's mandatory retirement age of 65 in 2017, but until he steps down, Tillerson retains control over one of the wealthiest and most influential companies on the planet.