Sigmund Freud developed psychoanalytic theory and proposed that personality has three parts: the id, ego, and super-ego. The id operates on the pleasure principle, seeking immediate gratification. The super-ego learns morality and tries to restrict the id. The ego acts as a mediator between the id and super-ego using the reality principle to satisfy id impulses in a way that considers social norms. Freud believed this three-part structure explained human behavior and development from childhood through adulthood.