In the surprise ouster and restoration of Sam Altman as chief executive officer at OpenAI, only one person, Adam D’Angelo, managed to play a role on each side of the drama. 

D’Angelo, a former Facebook executive and founder of the question-and-answer platform Quora, was one of four members of the board who fired Altman, and the sole surviving director named to a new board of the artificial-intelligence company that took over on Wednesday.