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Step aside, Bill Gates. Meet Mansa Musa I of Mali, a 14th century African king whose estimated $400 billion fortune makes him the richest human being in all of history, according to the website Celebrity Net Worth.

The website released a list last week of the wealthiest people who ever lived, claiming it had adjusted for inflation to bring the fortunes into 2012 dollars.

Microsoft founder Bill Gates, whose fortune peaked during the dot.com bubble at what would be $136 billion in today's dollars, ranks at No. 12, though he is now worth about half as much, according to the website.

The top 25 billionaires named have a combined fortune of $4.317 trillion. Fourteen out of the 25 are Americans, and none are women.

1. Mansa Musa I – $400 billion

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2. The Rothschild family – $350 billion

3. John D. Rockefeller – $340 billion

4. Andrew Carnegie – $310 billion

5. Nikolai Alexandrovich Romanov – $300 billion

6. Mir Osman Ali Khan – $230 billion

7. William The Conqueror – $229.5 billion

8. Muammar Qaddafi – $200 billion

9. Henry Ford – $199 billion

10. Cornelius Vanderbilt – $185 billion

Click here to see the entire list