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 being the primitive, unconscious part that seeks pleasure. Psychoanalysis aims to understand motivation by bringing the unconscious into conscious awareness using techniques like free association, hypnosis, and dream analysis.