Philip Zimbardo's 1971 Stanford University experiment, employing college students to play prison guards and inmates, became one of the most controversial episodes in modern psychology.

Philip G. Zimbardo, the psychologist behind the controversial “ Stanford Prison Experiment ” that was intended to examine the psychological experiences of imprisonment, has died. He was 91. Stanford University announced Friday that Zimbardo died Oct. 14 at his home in San Francisco. A cause of death was not provided.

Dr Zimbardo is remembered for an ill-fated 1971 prison study in which he recruited college-aged males to spend two weeks in a mock prison in the basement of a building on the Stanford campus.

The 1971 prison study was scheduled for two weeks, but was stopped after six days when college-aged students playing guards became psychologically abusive.