Sam Altman has been ousted as the head of artificial intelligence firm OpenAI by the company's board, which said it had lost confidence in his ability to lead the company.
The board said Mr Altman had not been "consistently candid with his communications", hindering its ability to exercise its responsibilities.
The 38-year-old helped launch OpenAI, which is behind the ChatGPT bot.
Mr Altman had become one of the most high-profile figures in the industry.
In a statement the board said it was grateful for Mr Altman's contributions but that members believed new leadership was necessary.
"The board no longer has confidence in his ability to continue leading OpenAI," the company said, citing "a deliberative review process by the board, which concluded that he was not consistently candid in his communications with the board, hindering its ability to exercise its responsibilities".
It is not clear what he is alleged to not have been candid about.
On social media, Mr Altman wrote that he had loved his time at the company.
"It was transformative for me personally, and hopefully the world a little bit. Most of all I loved working with such talented people," he wrote.
According to OpenAI co-founder Greg Brockman, it all took place over hastily-organised Google Meet video conference calls.
Mr Brockman - who was himself dismissed from the board a few minutes later and then resigned from the company - said both men were "shocked and saddened" by the news.
He said they were "still trying to figure out exactly what happened" but claimed in a post on X, formerly known as Twitter, that the whole drama unfolded in a matter of hours.
They sat on the company's relatively small board of just six executives. It is unusual for such a tight team to take such a dramatic decision so quickly, which begs the question: was it personal?
OpenAI is widely seen to be a company at its peak, with lucrative investment pouring in, and ChatGPT - which was launched almost exactly one year ago - is used by millions.
Mr Altman has been the face of the firm's rise. More than that, he is seen by many as the face of the industry more widely.
He testified before a US Congress hearing to discuss the opportunities and risks created by the new technology, and also at the world's first AI Safety Summit, held in the UK at the beginning of November.
The outpouring of support from Silicon Valley bosses shows that he enjoyed the support of the tech industry.
On social media, former Google boss Eric Schmidt called Mr Altman "a hero of mine" and said that he had "changed our collective world forever".
"I can't wait to see what he does next. I, and billions of people, will benefit from his future work- it's going to be simply incredible," he wrote.
There will be a lot of interest in whatever that next move is - and many will be waiting to see if Mr Altman is angry enough to talk about being dumped by the company he helped create.
He has promised he will have "more to say about what's next later".
But it doesn't appear he's poised to lift the lid on his departure just yet, even writing on X to advise OpenAI's remaining board members to "go after me for the full value of my shares" if he gets into a public row with them.
Mr Brockman announced he had quit his role at the company following Mr Altman's ousting.
In a statement posted X, Mr Brockman said: "I'm super proud of what we've all built together since starting in my apartment eight years ago.
"We've been through tough and great times together, accomplishing so much despite all the reasons it should have been impossible. But based on today's news, I quit."
He said he would continue to "believe in the mission of creating safe AGI that benefits all of humanity".
OpenAI started in 2015 as a non-profit. It restructured in 2019 and is now backed by Microsoft, which has invested billions.
Just weeks ago, OpenAI was reportedly in talks to sell shares in the company to investors at a price that would value it at more than $80bn (£64bn).
The company said its board members -who include an OpenAI chief scientist, the head of popular question and answer app Quora, and an AI researcher affiliated with Georgetown University - did not have shares in the firm and that their fundamental governance responsibility was to "advance OpenAI's mission and preserve the principles of its Charter".
The company said chief technology officer, Mira Murati, would take over as interim chief, effective immediately, while the board searches for a permanent replacement.
ChatGPT is known for its ability to respond to prompts from users with human-like text, images and videos.
Hundreds of millions of people have tried it out, and many are now regularly using it to help them do their jobs and study - to consternation in some cases, like teachers facing essays written by the bot and people worried for their jobs.
The company has also faced legal action from writers who say the bot developed its abilities by harvesting their work, in violation of copyright law.
Billionaire Elon Musk, who with Mr Altman was one of the founding co-chairs of OpenAI, has also criticised it for straying from its non-profit roots.
Source: BBC
