Leon Festinger was an American social psychologist, best known for developing the theory of cognitive dissonance in the 1950s. This theory explains how individuals strive for internal consistency and how they may change their beliefs or attitudes when faced with conflicting information. Festinger's work has had a significant impact on psychology, influencing areas such as attitude change, decision-making, and social behavior. In addition to cognitive dissonance, Festinger conducted important research on social comparison theory, which explores how people evaluate themselves by comparing to others. His studies have contributed to a deeper understanding of human behavior and the psychological processes that underlie social interactions.