Sam Altman is a billionaire—though perhaps not for the reason you think.

He is, in fact, the CEO of OpenAI, which is among the companies leading the $500 billion Stargate initiative focused on expanding artificial intelligence infrastructure in the U.S. But he doesn't own direct equity in that company, with most of his wealth instead coming from other investments.

Altman has an estimated net worth of $1.2 billion, according to Forbes. Here's how Altman made his money.

Tech Investments

Altman is one of Reddit's largest shareholders, and he served on the company's board until 2022. Altman had an 8.7% stake in Reddit, according to an SEC filing in February 2024 before Reddit's initial public offering (IPO) that March. Reddit had a market capitalization of $35.9 billion as of late January.

Altman's other investments include Airbnb, Uber, Instacart, Asana, and DoorDash, according to The Motley Fool.

He is also invested in the fintech company Stripe and nuclear fusion company Helion, according to Forbes. Stripe was valued at $70 billion in a November tender offer in November, according to Bloomberg.

OpenAI

OpenAI developed the popular AI chatbot, ChatGPT. Altman has been the head of the company since 2019; he was briefly fired by OpenAI's board in November 2023 and rehired a week later.

Altman does not own direct equity in OpenAI. Instead, he has an indirect interest in OpenAI through a small investment made before he was full-time by a fund in the startup accelerator company Y Combinator. Before joining OpenAI full-time, Altman was a partner at Y Combinator and was the company's president from 2014 to 2019.

Before he became the CEO, Altman was the co-chair of OpenAI when it was founded in 2015, along with Tesla CEO Elon Musk. While OpenAI initially started as a nonprofit research company with a focus on using AI "in the way that is most likely to benefit humanity as a whole," OpenAI launched a "capped" for-profit portion of the company managed by the nonprofit's board of directors in 2019.

ChatGPT was projected to bring in an estimated $2.7 billion in revenue for OpenAI for 2024, according to reporting last year by The New York Times. In October 2024, OpenAI was valued at an estimated $157 billion in a funding round in which it raised $6.6 billion.