In 2008 Mark Zuckerberg, founder of Facebook, was named the world's youngest billionaire, with a net worth of $4bn from his 24 per cent share of the company - not bad for a 26-year-old.
Zuckerberg created the site with his Harvard room-mates in 2004 and it now has 500 million active users. Despite concerns over privacy, the site has some of the world's heaviest traffic and is an essential tool for business, media and politics.
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