Sigmund Freud was an Austrian neurologist who founded the psychoanalytic school of psychology. He lived from 1856 to 1939. Freud developed theories about the unconscious mind and how unconscious desires and mechanisms influence our behavior and identity. He proposed that the mind can be divided into the id, ego, and superego, which represent unconscious, conscious, and moral components that sometimes conflict with each other. Freud's theories revolutionized the field of psychology and shaped our modern understanding of topics like sexuality, dreams, and the unconscious.