Widely considered to be the nineteenth centurys most influential revolutionary thinker, Karl Marx (1818-83) laid the theoretical foundations of modern socialism and communism. Born in Trier, Prussia (now part of Germany), Marx was educated primarily there and at the University of Berlin, receiving his doctorate in philosophy in 1841. Shortly afterward he met Friedrich Engels (1820-95), who belonged to the same circle of radical young Germans that Marx had joined as a student. Their friendship would ripen into one of historys most fruitful intellectual collaborations, with Marxs strong theoretical abilities complemented by Engelss practical knowledge and organizational skills. Though living and working mainly in Britain after 1848, they wrote in their native German. Their masterpiece would be the monumental Das Kapital (Capital, 1867-94). Like The Communist Manifesto, Das Capital was written largely by Marx but drew on theories that he and Engels had developed together, and two of its three volumes were edited by Engels for publication after Marxs death. Virtually all of the major ideas elaborated in Das Capital were first set forth in much shorter form in The Communist Manifesto. Their first major published work, it remains the most concise statement of an ideology that would ultimately change the course of history and hold sway over billions of lives.