He was technically a founding member, but left the company. Literally all of this is because he's jealous he can't pull a Tesla and claim all the credit for another tech company.
Wait... that's hilarious. He was part of openai? What kind of fucking idiot leaves that so early? I mean, maybe leaving this year for moral reasons... Sure. But he did this previously? What a fucking moron.
There was some internal dispute and he also claimed it was a conflict of interest with Tesla developing AI stuff. But I can't imagine how any conflict that may have existed with OpenAI doesn't exist with xAI