Jeff Bezos: $45.2 billion

The founder and CEO of Amazon.com helped revolutionize the retail industry by popularizing online shopping. What was initially an online book shop now sells pretty much anything. Bezos has reached beyond Amazon, in which he holds a 17 percent stake, to try his hand in other industries. He's bought the Washington Post and set up an aerospace company, Blue Origin, that aims to make space accessible to tourists and paying customers.