Philip Zimbardo knows what evil looks like. After serving as an expert witness during the Abu Ghraib trials, he wrote The Lucifer Effect: Understanding How Good People Turn Evil. From Nazi comic books to the tactics of used-car salesmen, he explores a wealth of sources in trying to explain the psychology of evil.

A past president of the American Psychological Association and a professor emeritus at Stanford, Zimbardo retired in 2008 from lecturing, after 50 years of teaching his legendary introductory course in psychology. In addition to his work on evil and heroism, Zimbardo recently published The Time Paradox, exploring different cultural and personal perspectives on time.

Still well-known for his controversial Stanford Prison Experiment, Zimbardo in his new research looks at the psychology of heroism. He asks, "What pushes some people to become perpetrators of evil, while others act heroically on behalf of those in need?"