4. Warren Buffett

•  Net Worth: $53.5 B                                                                       
•  Source of Wealth: Berkshire Hathaway                                       
•  Citizen:  United States
•  Age: 83 

 
Neither age nor prostate cancer slows Warren Buffett down: a year after completing radiation treatment, the world's fourth richest man ($58.5 billion) is still doing huge deals. His Berkshire Hathaway teamed up with 3G Capital to pick up iconic ketchup maker H.J. Heinz for $23.2 billion and a Berkshire subsidiary is buying Nevada's NV Energy for $5.6 billion. He gave away another $2 billion of Berkshire stock to the Gates Foundation in July, bringing his lifetime giving to nearly $20 billion.