Sigmund Freud, the father of psychoanalysis, proposed theories that emphasize the influence of the unconscious mind on behavior. He believed that the human mind was composed of three elements: the id, ego, and superego. The id is the primitive and instinctual part of the mind that contains sexual and aggressive drives. The ego is the realistic part that mediates between the desires of the id and the super-ego. The super-ego operates as a moral conscience. Freud also theorized that personality is shaped by childhood experiences, and he introduced the concept of psychosexual stages. His work has been influential in psychology, though not without controversy.