Sigmund Freud developed the first comprehensive theory of personality called psychoanalytic theory. He proposed that personality is formed by unconscious drives and motivations, especially those relating to childhood experiences and the resolution of psychosexual stages. According to Freud, the mind is divided into the conscious, preconscious, and unconscious. The unconscious contains unacceptable urges that are expressed through defense mechanisms. Freud also described personality as being comprised of the id, ego, and superego, and proposed five psychosexual stages through which a child's libido develops.