Sigmund Freud founded psychoanalysis and developed theories of the unconscious mind, personality structure, and psychosexual development. He proposed that the mind is divided into the conscious, preconscious, and unconscious levels. The personality consists of the id, ego, and superego. Psychic energy from the id is regulated by the ego and superego. Defense mechanisms like repression and reaction formation protect the ego from anxiety. The goal of psychoanalysis is to bring unconscious material into consciousness to resolve internal conflicts maturely.