Mark Zuckerberg
As Facebook has become ever more popular and prevalent worldwide, CEO and co-founder Mark Zuckerberg's image has taken some serious hits. The ubiquitous social network hit a new milestone — its 500 millionth member — but the world's youngest billionaire, at 26, had to defend himself against both personal and professional slights. Not only did Zuckerberg become a lightning rod in the debate over online privacy, with critics claiming that Facebook has no limits when it comes to revealing users' data, he was also the subject of a highly publicized film, The Social Network, a scathing account of the site's founding based on Ben Mezrich's book The Accidental Billionaires. Fortunately, Zuckerberg could take comfort in the real world, where Facebook's addicted users, and its projected 2010 revenue of $2 billion, may be the only real verdict that counts.