Karl Marx is a noted critic of capitalism. He was a German philosopher, economist, historian, sociologist, political theorist, journalist and revolutionary socialist. Marx's work in economics laid the basis for the current understanding of labor and its relation to capital, and has influenced much of subsequent economic thought. His most well-known works are 'The Communist Manifesto' and 'Das Kapital'. Marx's theories about society, economics and politics, collectively known as Marxism, hold that human societies progress through class struggle.