Pierre-Joseph Proudhon was a French politician, mutualist philosopher, economist, and socialist. He was a member of the French Parliament and the first person to call himself an "anarchist". He is considered among the most influential theorists and organizers of anarchism. After the events of 1848 he began to call himself a federalist.
Proudhon, who was born in Besançon, was a printer who taught himself Latin in order to better print books in the language. His best-known assertion is that Property is Theft!, contained in his first major work, What is Property? Or, an Inquiry into the Principle of Right and Government, published in 1840. The book's publication attracted the attention of the French authorities. It also attracted the scrutiny of Karl Marx, who started a correspondence with its author. The two influenced each other: they met in Paris while Marx was exiled there. Their friendship finally ended when Marx responded to Proudhon's The System of Economic Contradictions, or The Philosophy of Poverty with the provocatively titled The Poverty of Philosophy. The dispute became one of the sources of the split between the anarchist and Marxian wings of the International Working Men's Association. Some, such as Edmund Wilson, have contended that Marx's attack on Proudhon had its origin in the latter's defense of Karl Grün, whom Marx bitterly disliked, but who had been preparing translations of Proudhon's work.