CEO
Yahoo
2011 rank: 38
Age: 37
Mayer was in her 13th year at Google (and somewhat marginalized) when she leaped to the top job at Yahoo in July. Despite the web company's woes, it boasts $5 billion in revenue, $18 billion in market cap, and 700 million users -- a significant platform for this engineer to build on. And though she has much to prove, Mayer has already shown she can wield power by securing the Yahoo job on her own terms. (Her first child is due Oct. 7.)
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