Pierre-Joseph Proudhon (1809-1865) was a French philosopher and political economist, best known for his ideas on anarchism and socialism. He is often regarded as the first self-proclaimed anarchist, advocating for a society based on mutualism, where individuals and groups cooperate voluntarily without centralized authority. His famous declaration, "Property is theft," challenged traditional notions of ownership and capitalism. Proudhon's work influenced various political movements and thinkers, including Karl Marx and Mikhail Bakunin. He wrote several important texts, such as "What Is Property?" and "The System of Economic Contradictions," which explored the relationship between property, labor, and social justice. His ideas continue to resonate in contemporary discussions about anarchism and economic theory.