Mr Buffett, who is head of Berkshire Hathaway, is believed to have a fortune of around $62 billion after adding another $10 billion to his worth last year.
Known for his integrity, frugality and philanthropy, the 77-year-old American has given away 85 per cent of his money to charity since 2006 and still lives in the same house he bought when he was 28 for $31,000.
"Even though he is giving away a piece of his fortune each year, the stock of Berkshire Hathaway, the source of Warren Buffett's wealth, has been rising very rapidly," Forbes magazine's chief executive Steve Forbes commented.
In last year's annual letter to investors, Buffett said the secret to his success was to "be fearful when others are greedy, and be greedy when others are fearful".
Berkshire Hathaway is currently in the top ten most valuable companies, worth $215 billion.
Forbes claimed that Mr Buffett filed his first tax return at the tender age of 13, claiming $35 for the bicycle he used for his paper round.
Meanwhile, top US bankers have been erased from the list following the sub-prime crisis, including Lehman Brothers chief Richard Fuld and James Cayne who was sacked from the top job at Bear Stearns.