Robert Michels (1876-1936) was a German sociologist who wrote on the political behavior of intellectual elites and contributed to elite theory. He became a Socialist while teaching at the University of Marburg, and became active in the radical wing of the Social Democratic Party of Germany; he left the party in 1907. In 1914, Michels became a professor of economics at the University of Basel, where he taught until 1926. He is best known for his book Political Parties: A Sociological Study of the Oligarchical Tendencies of Modern Democracy (1916), which contains a description of the "iron law of oligarchy". Amongst his other works are Proletariato e la Borghesia nel Movimento Socialista Italiano (1908), Probleme der Sozialphilosophie (1914) and Imperialismo Italiano: Studi Politico- Demografici (1914).