Sigmund Freud is celebrated for his pivotal role in the development of modern psychology. He founded psychoanalysis, a revolutionary approach that explored the unconscious mind's influence on behavior and mental processes. Freud introduced concepts such as repression, defense mechanisms, and the Oedipus complex, which deeply influenced therapeutic practices and psychological theories. His work laid the foundation for understanding human behavior, and although controversial, it opened new avenues in psychotherapy and influenced various fields, including literature, art, and cultural studies, shaping the trajectory of psychological thought in the 20th century.