Sigmund Freud was an Austrian neurologist and the founder of psychoanalysis, a method for treating mental illness and understanding human behavior. He introduced concepts such as the unconscious mind, defense mechanisms, and the importance of childhood experiences in shaping personality. Freud's theories emphasized the role of repressed thoughts and desires in influencing behavior. Freud's work laid the foundation for modern psychology, although many of his ideas have been debated and revised over time. He developed techniques like free association and dream analysis to explore the unconscious. His influence extends beyond psychology into fields like literature, art, and cultural studies.