World's richest billionaires

POSTED: 07:56 AM PST Mar 08, 2012    UPDATED: 07:32 AM PST Mar 04, 2013 

A Mexican billionaire tops Forbes' world's richest list for a fourth year in a row.

Charles Koch
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6. Charles Koch (tie) -- Along with brother David, Charles is co-owner and executive vice president of Koch Industries, the second-largest privately held company in the U.S. He's worth an estimated $43 billion.

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