Sigmund Freud developed psychoanalysis in the late 19th century. He believed that human behavior is shaped by unconscious desires, memories, and conflicts that originate in childhood. Freud proposed that personality comprises the id, ego, and superego, and developed theories of psychosexual development and defense mechanisms. Psychoanalytic therapy uses techniques like free association and dream analysis to bring unconscious material to conscious awareness to resolve conflicts and better understand behavior.