Billionaire Elon Musk is expected to take the stand again in Oakland, California, in a landmark civil trial that could have a major impact on the development of artificial intelligence. On Tuesday, Musk accused OpenAI and its CEO Sam Altman of straying from its original nonprofit mission.

Elon Musk spent the better part of three days on the stand, accusing OpenAI and its executives of deceiving him into donating money to help found what is now one of the world’s biggest AI companies.

Elon Musk said in his second day of testimony that he was “a fool” for funding OpenAI. Mr. Musk grew combative during questioning from a company lawyer.

The trial comes at a pivotal moment for AI, a technology poised to bring advancement that could also drastically reshape humanity.

The blockbuster trial in Elon Musk’s lawsuit against OpenAI CEO Sam Altman may come down to a question of timing: Did he drag his feet before he sued over OpenAI’s for-profit conversion? Subscribe to read this story ad-free Get unlimited access to ad-free articles and exclusive content.

Musk's lawyers say OpenAI leaders "stole a charity" and Musk warns about the potential dangers of AI: "We don't want to have a Terminator outcome."

The bitter legal fight between Elon Musk and the leading artificial intelligence firm may come down to a few pages in one executive's personal notes.

Elon Musk, the Tesla CEO, world’s richest man and OpenAI cofounder, took the stand Tuesday in a high-stakes trial revolving around a bitter feud between himself and former friends Sam Altman and Greg Brockman that could reshape the future development of artificial intelligence.