Elon Musk vs. Jeff Bezos

Musk, who says he's worried about population collapse, has nine children with three women, including triplets and two sets of twins. As a kid in South Africa, Musk taught himself to code; he sold his first game, Blastar, for about $500.

Growing up, Bezos worked summers on his grandfather's ranch repairing Caterpillar tractors. Bezos met Google founders Larry Page and Sergey Brin in 1998 and managed to become one of the company's first angel investors, putting in an estimated $250,000.