Cameron and Tyler Winklevoss are best known for filing a giant lawsuit against Facebook founder Mark Zuckerberg and Facebook, claiming Zuckerberg stole his idea for the social network from their site, ConnectU. The battle began in 2004 and went on until 2008, when a cash-and-stock settlement deal was struck. (Even then, the appeals dragged on for another three years.)
The twins were granted 1.2 million Facebook shares in a deal valued at the time at around $65 million. Thanks to a five-for-one stock spilt, they're now sitting on 6 million shares -- a $228 million windfall.
Facebook's IPO will raise $16 billion, making it the third-largest IPO in U.S. history.