Sigmund Freud (1856-1939) was an Austrian neurologist who founded psychoanalysis, a framework for understanding the unconscious mind and its influence on behavior. He developed influential theories on repression, dreams, and psychological development, including the Oedipus complex. His major works, such as The Interpretation of Dreams, profoundly shaped psychology. Though controversial, Freud's ideas continue to inform debates about human motivation, psychotherapy, and cultural criticism.