How Elon Musk makes and spends his billions

Elon Musk may be the world's richest rocket scientist. With a fortune hovering around $20 billion, the 46-year-old CEO of Tesla and SpaceX and co-founder of OpenAI has said he won't be happy until we've escaped Earth and colonized Mars.

A notorious workaholic, Musk doesn't spend cash on lavish vacations or expensive hobbies. Instead, the entrepreneur spends most of his time at the office or in factories, retreating to one of his four Los Angeles mansions at the end of the day. Watch to find out what we know about how Musk, a father of five, amassed his fortune and how he spends it. Following is a transcript of the video.

He's been an entrepreneur since an early age. In college, he sold computer parts and would turn his house into a speakeasy on the weekends. After college, he and his brother founded Zip2, their version of an online yellow pages. In 1999, they sold the company and Elon made $22 million. He used that money to co-found X.com, an online banking service. X.com merged with a rival and became PayPal. eBay bought Paypal in 2002 and Musk made $180 million from the deal. He then went on to found SpaceX, Tesla, and Solar City. In 2009, Musk "ran out of cash" after divorcing his first wife. He lived off of loans while trying to keep his companies afloat.

That changed when Tesla IPO'ed in 2010. By 2012, Musk was a billionaire. He famously doesn't spend much on luxurious items, but he owns $70 million worth of homes in Los Angeles. He bought one of them for $17 million. It features a two-story library, home theater, gym, and wine cellar. Musk paid $920,000 for a submarine car used in the James Bond movie "The Spy Who Loved Me." He's also signed Bill Gates and Warren Buffett's "Giving Pledge," meaning most of his fortune will be left to charity.