Sigmund Freud was an Austrian neurologist who founded the psychoanalytic school of psychology. He is known for his theories of the unconscious mind, repression, and the psychodynamic approach. Some of his major theories included psychosexual development, the id/ego/superego model of personality, and the use of techniques like free association and dream analysis. Carl Jung was a Swiss psychiatrist who studied under Freud but later developed his own theories. Jung focused more on the collective unconscious and archetypes, and believed unconscious influences extended beyond sexuality.