Sigmund Freud (1856-1939) was an Austrian doctor who is considered the father of psychoanalysis. He believed that mental illness results from nurture rather than nature and that human motivation stems from unconscious drives and desires. Freud proposed that the human mind consists of the id, ego, and superego, with the id representing primitive, unconscious instincts and the superego acting as the conscience. Psychoanalysis aims to make the unconscious conscious through techniques like free association, hypnosis, and dream analysis to understand human behavior and resolve conflicts between desires and societal constraints.