Mark Zuckerberg, a ripe 27, is one of the least-known famous figures around. He's been the subject of books, profiles, gossip and paparazzi incursions; we know about his girlfriend, his house and, in tedious detail, his net worth; and a movie, "The Social Network," has been made about his social media startup Facebook, to interpretive controversy. Is he good, evil, crass or callow? What about those Winklevoss brothers? Through it all, he's been able to bury himself in work, apparently his abiding preoccupation, and sidestep much of the public glare: Facebook, after all, is private. But after years of speculation, Facebook, with its 800 million users and its aim to redefine privacy, has filed for its initial public offering, in which it will reportedly sell $10 billion worth of shares, valuing the company at $75 billion to $100 billion, and occurring anywhere from April to June. It will undoubtedly generate as much hype as Google Inc. -- last decade's big IPO -- once did, though it's unlikely to create a bubble, revive the IPO market or kick-start the U.S. economy. What it will do is make the downy-cheeked Zuckerberg CEO of a public company. Now he'll have to go public, too.

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