Pierre-Joseph Proudhon (1809–1865) was an economist, sociologist and a member of the French National Assembly. He played a central role in the International Working Men's Association and together with his opponent Karl Marx (1818–1883) he had a defining influence on the debates of the association. Proudhon's conflict with Marx ultimately resulted in a split in the IWA in 1872.
Pierre-Joseph Proudhon (1809–1865), ca. 1830, black-and-white photograph, photographer unknown; source: Archiv der sozialen Demokratie der Friedrich-Ebert-Stiftung Bonn, signature 6/FOTA099202.