Sigmund Freud was an Austrian physician and neurologist who founded psychoanalysis, focusing on the unconscious mind, repressive processes, and the interpretation of dreams. He developed significant theories, including free association as a therapeutic tool to access repressed emotions, and explored the intricacies of dreams, emphasizing the distinction between manifest and latent content. Despite health challenges and political exile, Freud's work left an enduring impact on psychology, demonstrating how unresolved unconscious conflicts influence mental health.