Ulrich Hansen, Germany (Journalist). · CC BY-SA 3.0

A computer scientist at MIT who built ELIZA, an early natural-language program that mimicked a psychotherapist by reflecting users' statements back as questions — and who was unsettled when people using it treated the program as if it understood them. That experience turned him into one of computing's earliest and most persistent critics of machines being mistaken for minds, a warning that reads as more prescient with each decade. The Weizenbaum Award and Weizenbaum Institute are named for him.