Elon Musk may be the world’s richest rocket scientist. With a fortune hovering around US$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 colonised Mars. Luckily, he has the mind and the money to make it happen.

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.

Scroll through to find out what we know about how Musk, a father of five, amassed his fortune and how he spends it.

As a child growing up in South Africa, Musk taught himself to code. By the time he was 12, he sold the source code for his first video game for US$500.

Just before his 18th birthday, Musk moved to Canada and worked a series of hard labour jobs, including shovelling grain, cutting logs, and eventually cleaning out the boiler room in a lumber mill for US$18 an hour – an impressive wage in 1989.

Musk got a pay cut to US$14 an hour when he started a summer internship alongside his brother, Kimbal, at the Bank of Nova Scotia after cold-calling – and impressing – a top executive there.

After he arrived for his freshman year at Queens University in 1990, Musk quickly picked up a side hustle selling computer parts and full PCs to other students. “I could build something to suit their needs like a tricked-out gaming machine or a simple word processor that cost less than what they could get in a store,” Musk said.

Within two years, Musk transferred to the University of Pennsylvania on a partial scholarship. To cover the rest of his tuition, Musk and a buddy would turn their house into a speakeasy on the weekends, charging US$5 at the door. “I was paying my own way through college and could make an entire month’s rent in one night,” Musk said.

Musk graduated with a bachelor’s degree in physics and an economics degree from the Wharton School and moved to Stanford to pursue his PhD. He left the programme within days to found an internet start-up with his brother. They started Zip2, a city guide software for newspapers, with US$28,000 in seed money from their father.

Four years later, in 1999, they sold Zip 2 for US$307 million, earning Musk US$22 million. He invested more than half of his earnings to cofound X.com, an online banking service. The company quickly merged with its rival and became PayPal with Musk as the majority shareholder. In 2002, eBay bought PayPal and Musk walked away with US$180 million.

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Musk turned his attention to his new space exploration company, SpaceX, after leaving PayPal. A few years later he cofounded electric-car maker, Tesla, and then SolarCity, a solar power systems provider. The success of these companies eventually launched him into the billion-dollar club – but not before he went broke.

In late 2008, Musk divorced his first wife and it took a toll on his finances. A year later, Musk said he “ran out of cash” and had been living off loans from friends while trying to keep his companies afloat. But when Tesla debuted on the stock market in 2010, Musk’s fortune sky rocketed. By 2012, he appeared on Forbes’ richest list for the first time with a net worth of US$2 billion.

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More than five years later Musk has amassed a US$20.4 billion fortune – and he’s not shy when it comes to spending it.

The CEO owns more than US$70 million worth of residential property in the Bel-Air neighbourhood of Los Angeles. His fifth and latest home purchase: a US$24 million as-of-yet unfinished estate.

Musk initiated his Bel-Air buying spree in late 2012, when the then-bachelor purchased a 1.67-acre estate for US$17 million. The 20,248-square-foot mansion has a two-story library, a home theatre, a gym, and 1,000-bottle wine cellar.

As the leader of one of the pre-eminent auto-makers, it’s no surprise Musk has an affinity for cars. Back in 2013, he paid US$920,000 at an auction for the Lotus Esprit submarine car used in a James Bond movie. In addition to driving Teslas, he owns two gas-powered cars: a Ford Model T and a Jaguar E-Type Series 1 Roadster.

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Despite having funds to spare, Musk isn’t a fan of lavish vacations – or any vacations for that matter. In 2015, he said he’d only taken two weeks off since founding SpaceX about 12 years earlier. He reportedly works 80 to 90 hours a week.

But he always carves out time for his kids. “I’m a pretty good dad,” Musk said. “I have the kids for slightly more than half the week and spend a fair bit of time with them. I also take them with me when I go out of town.” According to a 2014 tweet, Musk said he and his five sons go on an annual camping trip.

Space Family

A post shared by Talulah Riley (@talulahrm) on Nov 24, 2013 at 4:44pm PST

In 2012, Musk signed the Giving Pledge vowing to donate the majority of his wealth during his lifetime. Though he’s already in the business of improving our environment and the future during his day job, Musk has made sizeable donations to causes he cares about, including a US$10 million gift to the Future of Life Institute to regulate artificial intelligence.

At the end of the day, the multi-billionaire enjoys inexpensive hobbies like listening to music, playing video games, and reading books. “Hang out with kids, see friends, normal stuff,” he said. “Sometimes go crazy on Twitter. But usually it’s work more.”

Read the original story at Business Insider