Slim, 71, first showed a business talent as a 10-year-old selling drinks and snacks to his family. After studying engineering, he founded a real estate company and worked as a trader on the Mexican stock exchange. Cigar-smoking Slim is known for a "Midas touch" in acquiring struggling firms and turning them into cash cows. His enormous wealth contrasts starkly with his frugal lifestyle. He has lived in the same house for about 40 years and drives an aging Mercedes Benz, although it is armored and trailed by bodyguards. He has become involved in combating poverty, illiteracy and poor healthcare in Latin America and promotes sports projects for the poor, but has never voiced plans to give away large chunks of his wealth to charity. 2. Bill Gates (USA) - $56 billion, Microsoft
Sensing the start of a personal computer revolution, Gates, 55, dropped out of Harvard University in 1975 to start Microsoft and pursue a vision of a computer on every desk and in every home. Microsoft went public in 1986 and by the next year, the soaring stock made Gates, at age 31, the youngest self-made billionaire. In 2008 he stepped down from what is now the world's largest software firm to work at The Bill and Melinda Gates Foundation. He has given $28 billion to it. Together with his wife Melinda and Warren Buffett, he has also convinced 57 U.S. billionaires to sign up to the Giving Pledge and publicly vow to give away at least 50 percent of their fortune during their lifetime or upon their death. 3. Warren Buffett (USA) - $50 billion, Berkshire Hathaway
Buffett, 80, has run his Omaha, Nebraska-based conglomerate since 1965. Its interests run from railroads to ice cream. In 2006 he pledged to give away 99 percent of his wealth to the Bill and Melinda Gates Foundation and family charities. So far he has given $8 billion to the Gates Foundation. 4. Bernard Arnault (France) - $41 billion, LVMH
Arnault, 62, a friend of French...