Sigmund Freud, the father of psychoanalysis, developed influential and controversial theories about the unconscious mind, free association, and dream analysis, shaping our understanding of human behavior and mental processes. His framework includes distinct levels of the mind—conscious, preconscious, and unconscious—along with the dynamics of personality structured around the id, ego, and superego. Despite critiques of his ideas, Freud's concepts continue to influence psychology, particularly in understanding the complexities of human emotions and instincts.