Sigmund Freud is known for his work in psychoanalysis. He founded this school of thought in the late 19th and early 20th centuries, focusing on the unconscious mind's role in shaping behavior and personality. Freud introduced concepts such as the id, ego, and superego, which describe different aspects of the psyche. His theories revolutionized our understanding of the human mind and emphasized the importance of childhood experiences in adult psychological development. Despite facing criticism and evolving perspectives in psychology, Freud's influence is profound, and his ideas continue to impact modern therapy practices.