In his second day on the stand, Elon Musk was at times combative under questioning by OpenAI's lawyer, whom he accused of asking overly complicated questions.

"Your questions are not simple," he told lawyer William Savitt at one point. "They're designed to trick me essentially,"

Musk is suing fellow OpenAI co-founder Altman and the AI firm, alleging they misled him by shifting the organisation away from its non-profit roots toward a for-profit model.

OpenAI says Musk is motivated by jealousy and regret for walking away from the company in 2018. It has also accused Musk, head of xAI, of trying to derail one of his key rivals.

In the courtroom, Musk, wearing a dark suit and tie, started his testimony as Altman and OpenAI co-founder and president Greg Brockman, who is also being sued, looked on in the front.

Musk acknowledged that he had intended to have initial control over OpenAI but added he expected to have that control change quickly as more investors got involved.

The tech billionaire said he wanted to ensure the company was headed in the right direction early on because he was providing almost all the capital for it.

Noting that he has created many for-profit companies, Musk said, "I could have done that with OpenAI, but I chose not to. I chose something that was for the public benefit."

"I deliberately chose to create this as a non-profit for the public good."

Musk is asking for billions of dollars in what his lawyers call "wrongful gains" that he wants used to fund OpenAI's non-profit arm, and he wants to see a shake-up at the company including the ousting of Altman.

OpenAI has said Musk is using the lawsuit to derail one of his key competitors in the AI race, despite trying to portray himself as a paragon of safety and regulation.

In court, Savitt tried to poke holes in Musk's argument that he wanted OpenAI to remain a non-profit due to his concerns about Artificial General Intelligence - the kind of AI that surpasses human intelligence - falling into the wrong hands.

A year after OpenAI released the wildly successful ChatGPT, Musk launched a competing AI startup, xAI.

Savitt highlighted Musk's decision to launch xAI, the maker of the chatbot Grok, as a for-profit company.

The case, which could have far-reaching implications for the industry, is expected to last several weeks.

The head of Tesla's claims include breach of charitable trust and unjust enrichment.

The case stems from a lawsuit filed by Musk in 2024, accusing Altman, Brockman, and Microsoft, which has invested billions of dollars into OpenAI, of betraying the company's original non-profit mission.

Musk has criticised OpenAI's move to create a commercial arm, in 2019, years before launching ChatGPT and igniting the AI market.

The billionaire's own platform, xAI, has lagged behind competitors. The company launched in 2023, one year after ChatGPT hit the market.

OpenAI has argued that Musk understood the decision to open a commercial arm, and that he left the company only after failing to be granted control.

Musk donated $38m to the OpenAI non-profit, which the firm has maintained was "spent exactly as intended and in service of the mission".

On Tuesday in his opening statement, Musk outlined what he felt the lawsuit was about to one of his lawyers as he took the stand.

"It's actually very simple," he said. "It's not okay to steal a charity... If it's okay to loot a charity, the entire foundation of charitable giving will be destroyed."

Savitt, an OpenAI lawyer, said the lawsuit was motivated by Musk seeking to kneecap a "competitor".

He said that Musk had used his investment to "bully" other OpenAI founders, and that he had wanted to merge the company with Tesla, which he also owns.

"We're here because Mr Musk didn't get his way at OpenAI," said Savitt. "Because he's a competitor, Mr Musk will do anything to attack OpenAI."

Altman is also expected to testify during the trial.