After minting his fortune during the Internet boom of the late nineties, Elon Musk is building businesses in three 21st-century industries: space exploration, solar power, and electric automobiles. While there may be wealthier entrepreneurs who are still in their thirties, few can match the breadth or audacity of Musk’s vision.

In 1999, at the age of 27, the South African native sold his Internet software company Zip2 to Compaq for $300 million. He then co-founded PayPal, the online payment method now used by more than 20 million people. E-Bay purchased PayPal for $1.5 billion in 2002. Now Musk is primarily focused on space exploration as the CEO and chief technology officer of SpaceX, an aerospace company with ambitions to offer trips to the International Space Station and, ultimately, to enable humans to colonize Mars. As the chairman of Tesla Motors, Musk is behind the Tesla Roadster, a battery-powered sports car that accelerates from zero to 60 miles per hour in four seconds with zero emissions. Tesla’s next project is an all-electric sedan. Musk is also the chairman of SolarCity, a solar-panel-installation company. In just one year, SolarCity has become one of the biggest installers of home solar panels in the U.S.