Karl Marx (1818-1883) was a German philosopher, economist, and revolutionary socialist who co-authored "The Communist Manifesto" with Friedrich Engels, a foundational text for modern communism. Marx developed a comprehensive theory of history and society called historical materialism, which posits that social and economic conditions shape human societies and their development. He critiqued capitalism's inherent contradictions and injustices, arguing that it would eventually be replaced by socialism and ultimately communism, a classless, stateless society.