Bill Gates, Microsoft

Gates, 58, who co-founded Microsoft with Paul Allen, topped the list of the world's richest billionaires, with an estimated net worth of $76 billion.

He had previously stepped away from much of his day-to-day duties at Microsoft, with his last full day nearly six years ago. Following the retirement of former CEO Steve Ballmer, and the ushering in of new CEO Satya Nadella, Gates also gave up his position as chairman. 

Instead, he will serve as Nadella's technology advisor, a new post created specifically for Gates.

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