Karl Marx was a German philosopher, economist, and revolutionary socialist whose ideas formed the basis of Marxism. In 'The Communist Manifesto' (co-authored with Friedrich Engels) and 'Das Kapital,' he argued that human history is the story of class struggle between the ruling class (bourgeoisie) and the working class (proletariat). He predicted that capitalism would eventually collapse due to its internal contradictions, leading to a classless, stateless society. Marx's theories provided the ideological framework for the 20th-century communist revolutions in Russia, China, and beyond, making him one of the most influential figures in modern history, despite the varying ways his ideas were interpreted and implemented.