Microsoft co-founder Bill Gates reclaimed the title of world's richest person. He is the richest person in the U.S. for the 20th year in a row, according to <a href="http://onforb.es/1bmyB2T"target="external">Forbes</a>. Worth an estimated $72 billion, Gates, co-chair of the Bill and Melinda Gates Foundation, beat Carlos Slim, chairman of Grupo Carso in Mexico, for the world title.

Berkshire Hathaway CEO Warren Buffett is the second richest person in the 2013 Forbes 400 list as the biggest dollar gainer this year, after adding $12.5 billion to his net worth. He is now worth an estimated $58.5 billion.

Oracle Corp. CEO Larry Ellison is worth an estimated $41 billion, making him the third wealthiest person in America, Forbes says.

Charles Koch, 77, chairman and CEO of Koch Industries, and the fourth richest person in the country, tied with his younger brother, David Koch.

David Koch, executive vice president of Koch Industries Inc., 73, tied with his brother Charles for an estimated net worth of $36 billion.

Producer Christy Walton, 58, is the wealthiest woman in the world, according to Forbes, and the sixth richest person in the country. She is worth an estimated $34.5 billion. Walton inherited wealth after her husband John Walton, died in an airplane crash in 2005. Her father-in-law was Sam Walton, founder of Wal-Mart.

Jim Walton, chairman and chief executive officer of Arvest Bank Group Inc., is the youngest son of Wal-Mart founder Sam Walton. Walton, 65, is worth an estimated $33.8 billion, according to Forbes.