On Nov. 17, Silicon Valley tumbled into turmoil when Sam Altman, chief executive of the high-profile A.I. start-up OpenAI, was suddenly removed by the company’s board of directors. After a five-day roller-coaster ride that encapsulated the increasingly heated battle over the future of artificial intelligence, Mr. Altman was reinstated and a new board was created. Here is a list of players in the year’s biggest tech drama:

Sam Altman, OpenAI’s chief executive and a founder: Mr. Altman founded OpenAI as a nonprofit lab with Elon Musk and several others in 2015, while serving as the president of Y Combinator, a powerful Silicon Valley start-up incubator. He took over as chief executive in 2018, attached the lab to a for-profit company and soon raised $1 billion in funding from Microsoft.

Greg Brockman, OpenAI’s president and a founder: After dropping out of the Massachusetts Institute of Technology, Mr. Brockman was the chief technology officer at Stripe, an online payment company that Mr. Altman helped incubate. He was among OpenAI’s 12 founders, saying the lab would build A.I. that was free from the corporate pressures that drove Google and other tech giants.