Bill Gates: $75 billion

The man whose name is a byword for billionaire. He co-founded Microsoft in the mid-70s, growing it into the world's biggest software company and helping to make computers a household item. He quit as CEO in 2000 and pledged to devote his fortune to his philanthropic activities in the Bill and Melinda Gates Foundation. He has gradually reduced his ownership in Microsoft to less than 3 percent, with the bulk of his wealth in a private firm.