Philip Zimbardo, Psychologist Behind Stanford Prison Experiment, Dies at 91

The 1971 experiment is a cautionary tale that ordinary people can do terrible things under the right circumstances.

Philip Zimbardo attends the New York premiere of "The Stanford Prison Experiment" at Chelsea Bow Tie Cinemas in New York City on July 15, 2015. Andrew H. Walker/Getty Images

Philip Zimbardo, the renowned psychologist whose controversial Stanford Prison Experiment explored how social situations influence individual behavior, has died at the age of 91.

Stanford University, where Zimbardo was a professor emeritus of psychology, announced his death on Oct. 18. An obituary on his personal website states that he died peacefully at his San Francisco home on Oct. 14, surrounded by his wife and children.