Pierre-Joseph Proudhon: Pierre-Joseph Proudhon (1809-1869) was one of the most important and influential political theorists of the 19th century. The first person to call himself an anarchist, he is the author of What is Property? An Inquiry into the Principle of Right and of Government; The System of Economical Contradictions (or, the Philosophy of Misery); and The General Idea of the Revolution in the Nineteenth Century.