Leon Festinger was a hugely inspirational social psychologist, and is best known for his theory of cognitive dissonance. He taught at numerous US university including Stanford University. He died in 1989, aged 69.Henry W. Riecken was a professor of social psychology at the University of Minnesota when he co-authored When Prophecy Fails. He is the author of Social Experimentation and articles on the general topic of evaluating the effectiveness of educational and social programs.