Chairman and CEO, Berkshire Hathaway
Barely slowed by radiation treatments for stage 1 prostate cancer, Buffett has been on the hunt for big takeover candidates this year -- he's amassed a near record amount of cash, $47.8 billion -- but has so far held himself to small acquisitions including party favor company Oriental Trading and a newspaper in Waco, Texas. Buffett's complaint that his assistant pays a higher tax rate than he does became fodder earlier this year for President Obama's "Buffett Rule" -- and the topic of tax rates for the wealthy will surely continue to be a subject of intense debate. As evidence that investors can't get enough of Buffett's wisdom, more books featuring his insights are forthcoming this year, including Tap Dancing to Work, compiled by Carol Loomis, Fortune senior editor-at-large. --EF
He's a pro-customer, tightfisted risk-taker who is conditioning Wall Street to embrace his erratic earnings. If you're running a business with high margins - watch out.