OpenAI CEO Sam Altman has begun his testimony against Elon Musk in a high-profile jury trial in a California federal courtroom.

Altman, alongside OpenAI president Greg Brockman, is a primary defendant in the trial brought by Musk. Altman, Brockman, and Musk were all part of the initial founding team at OpenAI, with Musk investing up to $38 million in the ChatGPT-maker’s early days. But the relationship between Musk and other OpenAI founders eventually soured, and Musk stepped away from the company, later going on to found his own direct competitor, xAI. In recent years, Musk and Altman have traded barbs and made a slew of allegations against each other, driven largely by Musk’s handful of legal actions against OpenAI, many of which have since been dropped or dismissed.

The Musk v. Altman trial has already drawn testimony from prominent AI industry leaders including Brockman; Microsoft CEO Satya Nadella; former OpenAI board member (and mother of Musk’s children) Shivon Zilis; and former OpenAI CTO (and, briefly, CEO) Mira Murati, who is now founder of her own AI startup, Thinking Machines Lab. Musk is calling for a number of remedies, including asking the court to strip both Altman and Brockman of their roles and to unwind OpenAI’s for-profit restructuring.