X owner and Tesla CEO Elon Musk took the stand to testify against OpenAI CEO Sam Altman on Tuesday in his lawsuit against the ChatGPT parent company.

Musk, who helped co-found OpenAI with Altman and a group of tech industry leaders, is suing his former business partner and company, arguing that OpenAI has deviated from the humanitarian mission it was initially founded on. Musk has taken issue with the fact that Altman transitioned OpenAI away from its nonprofit model to a for-profit company, arguing that Altman prioritized monetary gain over the original beneficial mission.