Sigmund Freud (1856-1939) was an Austrian neurologist who founded the psychoanalytic school of psychology. He is best known for his theories of the unconscious mind and the defense mechanisms. Freud believed that unconscious desires and motivations determined behavior. He proposed that personality develops through psychosexual stages in childhood and proposed defense mechanisms help manage anxiety from conflicts between the id, ego, and superego. Freud developed psychoanalysis as a therapeutic technique using free association and dream analysis to reveal the unconscious.