Carl Icahn is a billionaire some 24 times over. He made his fortune on Wall Street, where he likes to build a significant stake in troubled companies -- and then leverage it to force big changes. Some think of him as the perfect antithesis to Berkshire Hathaway guru Warren Buffett, but there's no question that his methods work. Icahn has the numbers on his side.

Sometimes he wants to install new management, as he did at Blockbuster 10 years ago. Other times, he goes for a hostile takeover, like the one he attempted on Lionsgate (NYSE:LGF-A) in 2010.

Apple is too big for even a billionaire activist to make any truly fundamental changes, but Icahn still helped convince Cupertino to make massive increases to its buyback program.

Of course, he isn't opposed to simply making a ton of money when he sees a "no-brainer" opportunity, as he's currently doing in Herbalife (NYSE:HLF). And he doesn't win every battle or nail every analysis, but Carl Icahn will often find a way to make money even when he's wrong. Netflix (NASDAQ:NFLX) is a recent case in point, having bagged Icahn $800 million (and counting).

How well do you know this controversial investor? Is he a shareholder hero, or just a heartless corporate raider? This slideshow will help you fill in the blanks.

How well do you know activist billionaire Carl Icahn? from The Motley Fool.