Among the many unusual facts about OpenAI, the buzzy startup behind the hugely popular chatbot ChatGPT, the most extraordinary may be that Sam Altman, its CEO and co-founder, doesn’t have any equity in it. He gave up the opportunity for a huge potential payday, he says, simply because he doesn’t need the money.

But Altman, 38, has a head-spinning number of investments in plenty of other companies he believes will make him a lot more money in the future. Over the past decade, he has become one of Silicon Valley’s most prodigious angel investors, making around 400 investments in companies such as Reddit, Stripe and Asana, along with AI startups like Cerebras and Humane.

He has made many of his investments through Hydrazine Capital, a San Francisco–based venture firm he founded that invests capital from him as well as others like Peter Thiel, and through Apollo Projects, an investment fund he launched with his brothers, Jack and Max Altman.