Karl Marx was a German philosopher, political theorist, economist, journalist, and revolutionary socialist. He is best-known for the 1848 pamphlet The Communist Manifesto (written with Friedrich Engels), and his three-volume Das Kapital (1867–1894), a critique of classical political economy which employs his theory of historical materialism in an analysis of capitalism.

Born in Trier in the Kingdom of Prussia, Marx studied at the universities of Bonn and Berlin, and received a doctorate in philosophy from the University of Jena in 1841. A Young Hegelian, he was influenced by the philosophy of Georg Wilhelm Friedrich Hegel, and both critiqued and developed Hegel's ideas. While in Paris, Marx wrote his Economic and Philosophic Manuscripts of 1844 and met Engels, who became his closest friend and collaborator. Together, they wrote The Communist Manifesto, which expresses Marx's ideas and lays out a program for revolution.

Marx was expelled from Belgium and Germany, and in 1849 moved to London, where he wrote The Eighteenth Brumaire of Louis Bonaparte (1852) and Das Kapital. From 1864, Marx was involved in the International Workingmen's Association (First International), where he opposed the influence of anarchists led by Mikhail Bakunin. In his Critique of the Gotha Programme (1875), Marx wrote on revolution, the state, and the transition to communism.

Marx's critiques of history, society, and political economy hold that human societies develop through class conflict. In the capitalist mode of production, this conflict occurs between the bourgeoisie who control the means of production and the proletariat who enable these means by selling their labor power for wages. Marx predicted that capitalism would produce internal tensions leading to its self-destruction and replacement by socialism. Ultimately, he envisioned the establishment of a classless, communist society.

Marx has been described as one of the most influential figures of the modern era, with his work exerting major influence on socialist thought and political movements. Marx's work in economics has had a strong impact on modern heterodox theories of labor and capital, and he is often cited as one of the principal architects of modern sociology.