Go inside the Tesla Model S and see what makes it special.
Tesla shares have soared more than 180% this year, with the firm reporting its first-ever quarterly profit earlier this month. SolarCity shares debuted on the Nasdaq in December at an IPO price of $8 and are now worth six times that, closing Friday at $48.78.
As the largest shareholder in both companies, Musk has richly benefited from their rallies.
As of December 31, he owned 33.1 million Tesla shares, including 5.9 million issuable upon the exercise of options, according to securities filings. That stake is now worth .24 billion, an increase of .1 billion since the start of 2013.
As of mid-April, he owned 20.8 million SolarCity shares. They're now worth .02 billion, an increase of nearly 7 million since the start of the year.
Tesla and SolarCity declined to comment on Musk's holdings.
It's difficult to estimate Musk's overall net worth precisely. He's also a major investor in privately held SpaceX, a commercial space exploration company he heads and co-founded, and has been involved in several venture-capital and private-equity partnerships, according to VentureBeat.
Musk previously co-founded online payment service PayPal, which eBay acquired in 2002, and software firm Zip2, which Compaq bought in 1999. He used some of the proceeds from those sales to fund SpaceX and Tesla - founded in 2002 and 2003, respectively - in their early stages.
"If I did not take these loans, I would have no liquid assets left, " he said.
His situation has improved since then. Tesla's first-ever profit came after sales of the company's luxury Model S plug-in came in ahead of expectations. Consumer Reports called the Model S the best car it had ever reviewed.
SolarCity reported earlier this month that its customer base had grown 106% versus a year ago to over 57, 400, while revenue rose 21%. SpaceX - which has been the subject of IPO chatter - became the first commercial venture to successfully attach a vehicle to the International Space Station last May, and repeated the feat in October.
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