Suchir Balaji, a former OpenAI engineer and whistleblower who helped train the artificial intelligence systems behind ChatGPT and later said he believed those practices violated copyright law, has died, according to his parents and San Francisco officials. He was 26.

Balaji worked at OpenAI for nearly four years before quitting in August. He was well-regarded by colleagues at the San Francisco company, where a co-founder this week called him one of OpenAI’s strongest contributors who was essential to developing some of its products.