OpenAI president Greg Brockman has described a heated 2017 meeting with Elon Musk over the billionaire's early attempt to control the artificial intelligence (AI) company.

Brockman, a co-founder of OpenAI and a defendant in Musk's lawsuit seeking to undo its transition to a for-profit business, told a jury in Oakland federal court that when he rejected a proposal to give Musk more say in the company, Musk's mood abruptly changed.

"I actually thought he was going to hit me," Brockman said, referring to Musk.

The meeting ended shortly thereafter, Brockman said, with Musk announcing that he would start withholding funding from OpenAI, which he had backed since its launch in 2015.

Brockman's testimony comes during the second week of a month-long trial between Musk and OpenAI's key founder and chief executive, Sam Altman.

It is part of a bitter feud that has grown over the years since Musk left OpenAI, where he was among the initial co-founders, and has watched as the AI company became one of the most valuable tech enterprises in the world after its launch of ChatGPT.

Before Musk decided to exit OpenAI, Brockman described his attempts to gain more control over the company, an effort that included "buttering up" Brockman and another co-founder, Ilya Sutskever.

Lawyers for OpenAI showed text messages from August 2017 between Sutskever and Brockman that said: "Will a model 3 make you be willing to accept massively unfavourable terms?"

The crux of Brockman's testimony so far has been that Musk was aware of plans to shift OpenAI to be more of a traditional for-profit business.

When the company started, it was a non-profit, then it added a for-profit arm to raise billions of dollars for investors, before deciding last year to make the for-profit part of the company the focus.

Brockman's appearance in court is expected to be followed by former OpenAI board member Shivon Zilis, who is the mother of four of Musk's children.

Brockman testified that Zilis informed him she had had twins, but that he only found out later from public reports that Musk was the father.

Brockman said when he spoke with Zilis after learning Musk had fathered her twins, "she said that it was via IVF and that it was entirely platonic with Elon."

When asked about Zilis' involvement with OpenAI for years after Musk had left the company, Brockman said: "We trusted her to keep the Elon conflict under control."

Zilis left the board in March 2023 as Musk was launching xAI, an AI company developing a chatbot that directly competes with OpenAI's ChatGPT.