Elon Musk took the stand for a second day of testimony against OpenAI and its leaders in a lawsuit that could reshape the future of artificial intelligence, as the emerging technology has sent ripples through the economy and financial markets.

It was 2018, and Elon Musk was having a very busy year.

“I came up with the idea, name, recruited the key people, provided the funding,” he said in court.

The $25 billion estimate that a top Pentagon official gave to lawmakers on Wednesday for the total cost to date of the Iran war is a lowball figure that does not include the cost of repairing extensiv...