OpenAI co-founder Greg Brockman has returned to the artificial intelligence startup three months after taking a leave from his role as president, bringing a key figure back to the C-suite amid an exodus of top executives. Brockman announced he has officially started working again at OpenAI in an internal memo to staffers on Tuesday, according to a person familiar with the matter, who spoke on condition of anonymity to discuss company matters. In his memo, Brockman said he has been working with C...