The title of world’s richest person can change on any given day, depending on corporate share prices—but as of late, that title has been held by Elon Musk. Famous for his business prowess, communication style, and role as a tech visionary, Musk has often been hailed as a genius.

Musk is the CEO and co-founder of Tesla (TSLA), the electric vehicle company, and the CEO and lead designer of the aerospace company SpaceX. Elon Musk has generated his wealth primarily through companies that he founded, but part of his fortune also comes from passive investments. Keep reading to learn which of Musk’s investments make it into the top five.

1. PayPal

In 1999, Musk co-founded X.com, an online financial services and email payment company. A year later, X.com merged with Confinity, which in 2001 was renamed PayPal (PYPL).

On Oct. 3, 2002, PayPal was purchased by eBay (EBAY) for $1.5 billion. At the time of the sale, Musk owned 7,109,989 shares of PayPal, which made him the largest shareholder with a stake of 11.7%.

Musk no longer holds a stake in PayPal. He exited his position after the sale of the company and used his proceeds from the sale to fund investments such as SpaceX, Tesla, and SolarCity.

2. SpaceX

In 2002, Musk founded Space Exploration Technologies Corp., commonly known as SpaceX. The company’s founding mission is to revolutionize space technology, including by developing spacecraft that carries humans to Mars and other places in the solar system.

NASA awarded SpaceX a lucrative contract in 2006. In 2008, SpaceX launched Falcon 1, the first private liquid-propellant rocket to reach orbit. In 2010, SpaceX’s Dragon spacecraft reached the International Space Station (ISS). In 2012, granted SpaceX a second contract to help shuttle crew members between the ISS and Earth.

Another contract with NASA was inked in 2021 for $2.9 billion, to transport astronauts aboard its Starship vehicles from lunar orbit to the surface of the moon.

3. DeepMind Technologies

The artificial intelligence (AI) company DeepMind Technologies was launched in late 2010, with Musk as one of its key angel investors. In January 2014, Google announced that it had acquired the company for an undisclosed amount.

Musk is famously worried about AI overtaking humans and is reported to have invested in DeepMind not to make money but to stay abreast of how rapidly the technology behind AI is developing.

DeepMind has focused much of its research on deep reinforcement learning, which is an AI technique that combines deep learning—which is primarily for recognizing patterns—with reinforcement learning. DeepMind developed this type of learning based on reward signals, such as a score in a game, and gave the technique its name in a 2013 white paper.

Though developing deep reinforcement learning represented a breakthrough in AI, DeepMind hasn’t yet found many successful commercial applications. Alphabet, Google’s parent company, has applied the technique internally to reduce the power costs associated with cooling Google’s servers at data centers.

4. Tesla Motors

Musk was not a founding member of Tesla but led an early round of financing in 2004. In 2008, Musk went from being a board member of Tesla to its CEO, even while still serving as the CEO of SpaceX. On June 28, 2010, Tesla launched its initial public offering (IPO) on Nasdaq with shares of common stock initially available to the public at $17 per share. As of March 7 2022, shares of Tesla traded for more than $800.

Tesla’s mission is to accelerate sustainable transportation by introducing mass-market electric cars to the public. In November 2017, Tesla announced the creation of fully electric tractor-trailer trucks, which were preordered by companies such as United Parcel Service (UPS) and PepsiCo. The company’s electric vehicles include the Model S, the Model X, the Model 3, and the high-end Roadster supercar.

As of Dec. 28, 2021, Elon Musk owned 177 million shares of Tesla, worth approximately $142.3 billion. Elon Musk remains the company’s largest individual shareholder and has significant control over the company’s long-term plan and operational goals.

5. The Boring Company

Musk founded the infrastructure and tunnel construction company known as The Boring Company in 2017. The company was founded on the premise that traffic is awful but traveling above ground isn’t necessary—traffic woes could be “solved” by using the miles and miles of earth beneath roadways. The company’s goal is to reduce the cost of tunneling while also making production more efficient.

In March 2019, the Las Vegas Convention and Visitors Authority approved a $48.6 million proposal from The Boring Company to build an underground tunnel, called the LVCC Loop, that would travel underneath the Las Vegas Convention Center and feature three stations and a pedestrian tunnel. In April 2021, The Boring Company officially opened the LVCC Loop. As of 2022, The Boring Company has completed additional projects in Hawthorne, Calif., and currently has another project underway in Las Vegas.