Occupation: Co-founder, LinkedIn
Hoffman may be the most connected person in Silicon Valley, so it's fitting that the company he co-founded nearly a decade ago, LinkedIn, is the most important social network for business professionals. After LinkedIn's successful IPO last year, Hoffman became a billionaire. Now a partner at venture-capital firm Greylock, he is known as one of technology's savviest investors, with early stakes in Facebook and Zynga. In his recent book, The Start-Up of You, Hoffman offered career lessons informed by two decades in Silicon Valley.