The 400 richest Americans are the richest they've ever been, according to Forbes magazine.

The combined net worth of the people on the list hit a record $2.02 trillion, up 19% from last year's total of $1.7 trillion, thanks in large part to a strong stock market and a real estate recovery. The average net worth of members of this year's list is $5 billion, up $800 million from a year ago.

Microsoft (MSFT) founder Bill Gates took the top spot as the richest American for the 20th year in a row, with a personal fortune of $72 billion. Berkshire Hathaway's (BRKA) Warren Buffett came in second with a net worth of $58.5 billion. Buffett also posted the biggest dollar gains on this year's list, with his wealth climbing a staggering $12.5 billion.

Mark Zuckerberg also had a good year, thanks to the rebound in Facebook's (FB) share price. After dropping to number 36 last year, he returned to the top 20 with a personal fortune of $19 billion. His gain of $9.6 billion made him this year's second-biggest gainer.

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It took a lot more money to make this year's list, with the minimum net worth set at $1.3 billion. That meant that 28 people from last year dropped off the list, including T. Boone Pickens, whose wealth dipped to $950 million.

Forty-eight women also made the 2013 list, including Hyatt Hotels heiress Jennifer Pritzker, who was formerly known as James Pritzker, and is the first transgender billionaire, according to Forbes.

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Most of this year's billionaires had a good year: 314 members saw their fortunes climb this year, while only 30 members saw their net worth decline.