Elon Musk already had his hands full even before he finalized Monday’s $44 billion deal to take over Twitter. 

The entrepreneur — who now holds the title of world’s richest man — got his start in Silicon Valley after he dropped out of Stanford University in 1995 and co-founded PayPal, where he worked alongside other now-legendary entrepreneurs including Palantir co-founder Peter Thiel and LinkedIn co-founder Reid Hoffman.

In 2002, eBay acquired PayPal for $1.5 billion in stock, giving Musk a personal fortune of $175 million. 

Musk parlayed the PayPal money into a variety of far-flung ventures and now controls $1 trillion electric car company Tesla, space exploration firm SpaceX, brain implant startup Neuralink and tunnel construction firm the Boring Company.

On Monday, Musk added Twitter to his collection in a deal expected to close within months. He has also mulled combining all of his companies into a potential super-conglomerate. 

Here’s a look at Musk’s sprawling empire, which he hopes will one day stretch from implants inside people’s brains to the surface of Mars: 

Tesla 

While Musk has become synonymous with electric automaker Tesla, he did not found the company. 

Rather, he was the lead investor in the company’s 2004 series A funding round, becoming the company’s largest shareholder in exchange for $6.5 million. 

Musk assumed greater control over Tesla in subsequent years, becoming the company’s CEO in 2008 and overseeing the rollout of its first commercially available car, the Roadster, in 2009. 

While Tesla is still tiny in comparison to automakers like Ford and Toyota, the company is rapidly scaling up production and rocketed to “meme stock” status during the pandemic, surging from less than $100 at the beginning of 2020 to more than $1,200 at some points in 2021. It’s now the most valuable car company in the world.

Tesla has also acquired SolarCity, a solar energy firm Musk helped start in 2006 that has a production facility in Buffalo, New York. After Tesla bought SolarCity for over $2 billion in 2016, some disgruntled shareholders claimed in court that Musk had unfairly strong-armed Tesla’s board into approving the deal in order to save his cash-strapped and unprofitable solar firm. They are seeking billions from Musk in an ongoing suit in Delaware.

Tesla’s soaring valuation has made Elon Musk the world’s richest man, with an estimated net worth of $246 billion, according to Forbes. 

But most of Musk’s net worth is tied up in Tesla shares — not cash — which is why the mogul is using an unconventional financing plan to cover his purchase of Twitter that included borrowing money using his Tesla shares as collateral. 

SpaceX 

Musk founded SpaceX in 2002, around the same time eBay purchased PayPal, with a mission to make access to space faster and cheaper — and eventually create a colony on Mars. 

Musk personally interviewed every early employee of the company before he hired them, according to journalist Eric Berger. 

SpaceX has since inked deals with NASA and became the first private company to send astronauts into orbit and to the International Space Station. 

Musk serves as CEO of the company, which has launch facilities in Florida and Texas. 

In addition, SpaceX has launched an internet service called Starlink, which beams down internet access to far-flung areas of the world. 

The Ukrainian military has since used Starlink internet service to help fend off Russia’s invasion of the country. 

Neuralink

Musk secretly founded Neuralink in 2016 with a mission to create brain implants that will one day make humans hyper-intelligent, heal traumatic brain injuries and let paralyzed people walk again. 

He serves as the company’s CEO and has described its technology as a “FitBit in your skull.” He argues that the brain chips are needed in order for humans to keep pace with increasingly intelligent computers. 

Neuralink’s existence was kept secret until a Wall Street Journal report in 2017 — and the company shares relatively little information about its projects with the public. 

However, the company has nonetheless attracted its share of controversy. 

In 2020, the MIT Technology Review dismissed Neuralink as “neuroscience theater,” writing that Musk is making “promises that will be hard to keep” and risks being a disappointment. 

Animal rights activists have also accused Neuralink of subjecting monkeys to “extreme suffering,” writing in February of this year that at least 15 test animals had died in gruesome Neuralink experiments at the University of California, Davis. 

Neuralink has defended the tests and claims that it will start testing its technology n humans in 2022. 

The Boring Company

Musk started the Boring Company as a subsidiary of SpaceX in 2016 and spun it off into an independent company in 2018. 

The company’s mission is to construct “hyperloop” tubes that will shoot cars at high speeds between major cities, cutting down on highway congestion. 

The Boring Company has opened two short loops in Las Vegas and a test tunnel outside Los Angeles — but Musk has far greater ambitions. 

He claimed in 2017 that he had “verbal approval” from the US government to construct hyperloop between New York City and Washington, D.C. that would reduce travel time between the two cities to just 29 minutes. The Boring Company also said in 2018 that it was pursuing a hyperloop connecting downtown Chicago to the O’Hare Airport. But neither plan appears to have made progress since their initial announcements. 

Nonetheless, the Boring Company announced on Friday that it had raised $675 million at a valuation of nearly $5.7 billion from backers including venture capital firm Sequoia. 

Musk reiterated his commitment to the Boring Company in a tweet on Sunday, writing, “In the coming years, Boring Co will attempt to build a working Hyperloop.” 

“From a known physics standpoint, this is the fastest possible way of getting from one city center to another for distances less than ~2000 miles,” he claimed. “Starship is faster for longer journeys.” 

Twitter 

Twitter was co-founded in 2006 by Jack Dorsey, who’s a personal friend of Elon Musk. 

Musk joined the site in 2009 and became known as one of the site’s most popular and outspoken users, sharing everything from crude jokes about politicians to musings about space travel.

Twitter went public in 2013 and Musk hinted at plans to take it private for years. 

In 2017, Musk tweeted “I love Twitter.”