Sigmund Freud was a Czech neurologist who revolutionized how we think and treat mental health conditions. He became famous for inventing and developing the technique of psychoanalysis, a clinical method for evaluating and treating pathologies, through dialogue between a patient and a psychoanalyst. Freud's main theory suggests that human behavior is influenced by unconscious memories, thoughts, and urges. This theory also proposes that the psyche comprises three aspects: the id, ego, and superego. The id is entirely unconscious, while the ego operates in the conscious mind. He is considered among the most influential doctors of the 20th century, as he changed the way society views mental illness.