Larry Ellison: $43.6 billion

As a young programmer in the '70s, his first big client was the CIA. The name of the project was "Oracle." In 1977, Ellison and associates used the name of that product for their company, which creates software that helps manage databases and has since become an industry standard. Ellison has recently focused more on cloud computing, in which data is stored and managed across a network of computers. His fortune comes from the 27 percent stake he still owns in Oracle, currently worth $160 billion.