Sigmund Freud founded psychoanalytic theory and developed concepts like the unconscious mind, psychosexual development, defense mechanisms, and the id, ego, and superego model of personality. Psychoanalytic therapy involves talking therapy where a therapist helps clients gain insight into unconscious motivations by exploring patterns from their past and present relationships. It aims to resolve deep-seated conflicts through understanding repressed feelings, thoughts, and memories from childhood. Variations like psychodynamic therapy are shorter-term and focus more on current problems.