20231122 Sam Altman
Sam Altman was known as one of the tech industry's most prolific angel investors, making dozens of investments in a range of companies focused on extending life to building fusion reactors. Image Credit: AP

Sam Altman is best known as the chief executive of OpenAI - the pioneering artificial intelligence company that has turned him into one of Silicon Valley's most powerful people. But before that, Altman was known as one of the tech industry's most prolific angel investors, making dozens of investments in a range of companies focused on extending life to building fusion reactors.

Now, his sprawling web of investments in start-ups is facing fresh scrutiny, as some of them do business with OpenAI or could benefit from preferential access to OpenAI's technology.

Since 2010, Altman has personally invested in 125 companies, according to venture capital research firm PitchBook. Other entities that he's associated with, including an investment firm he founded with his brothers called Hydrazine Capital, have invested in two dozen more. This year alone, as OpenAI grew rapidly under his leadership, he made more than 20 investments. From 2011 to 2019, Altman was also an investor at Y Combinator, Silicon Valley's most prominent start-up incubator, where he served as lead partner on another 280 deals, giving him influence among dozens of the most promising start-ups in tech.

Here are a few of the most notable investments in Altman's empire.

Helion Energy

Nuclear fusion has been a science-fiction fantasy for decades. Unlike regular nuclear reactors, which generate power by splitting atoms, fusion reactors do the same by smashing two atoms together. A recent breakthrough from US government scientists has ignited excitement that clean and cheap fusion energy may actually be possible. Despite those recent advances, many scientists and engineers are still skeptical that fusion will work any time soon. Several start-ups are trying to do it anyway, including Helion Energy. Altman invested in the Everett, Washington-based company as a partner at Y Combinator in 2014. Then in 2021, he invested $375 million in the company, according to venture capital data firm CB Insights, his largest personal investment ever.

In May, just months after investing billions of dollars in OpenAI, Microsoft signed a deal to be the first company to buy electricity from Helion, which it expects to begin producing in 2028.

Boom Aviation

Remember the Concorde jet? Boom Aviation is one of a small group of companies trying to bring back supersonic commercial travel more than 20 years after the Concorde made its last flight. Altman first invested in Boom as a private investor in 2016. Then, as a partner at Y Combinator in 2019, Altman invested in the company again. Boom has signed tentative purchase agreements for its still-under-development Overture jet with United and American Airlines and it plans to have the jets carrying passengers by 2029.

Retro Biosciences

The biotechnology company wants to slow aging by developing techniques to remove damaged cells and treating older cells to make them act as if they were young again. Altman invested $180 million in the company in 2022. Along with Helion, the two huge investments accounted for "all my liquid net worth," Altman told MIT Technology Review earlier this year. Despite the huge cash infusion, the company is still very early stage, announcing its presence to the world in 2022 when Altman made his investment.


Former Apple employees and married couple Imran Chaudhri and Bethany Bongiorno believe they've invented a new hardware device for the age of AI. Human's "Ai Pin" is worn on the chest and can be controlled by voice commands and hand movements. A laser display can be projected onto the user's hand, obviating the need for a screen. Altman has contributed to three of Humane's funding rounds, from 2020 to 2023. At the same time, he's invested in another similar hardware company, called Rewind AI.


The self-driving car company went through Y Combinator when Altman worked there, and he made a personal investment in 2015. The next year, General Motors acquired the start-up. Cruise is now one of the most prominent self-driving car companies, and it was the first to provide a driverless ride-hailing service in San Francisco. But the company is now in crisis. In October, a human driver hit a pedestrian, flinging her into the path of a Cruise car, which then rolled over the person and dragged her for 20 feet. California authorities accused Cruise of trying to cover up the details of the accident. The company lost its permits to operate in California and pulled its entire self-driving fleet off public roads. In November, Chief Executive Kyle Vogt stepped down.