Philip Zimbardo is an American psychologist best known for his role in the Stanford prison experiment conducted in 1971. This study examined the psychological effects of perceived power by assigning college students to the roles of guards and prisoners in a simulated prison environment. The experiment revealed how situational factors can influence behavior, leading to unexpected and often troubling outcomes. Zimbardo has also contributed to the fields of social psychology and the study of time perspective. He has written several books, including The Lucifer Effect, which explores the nature of evil and how ordinary people can commit harmful acts under certain conditions.