The correct answer is author and philosopher.
Karl Marx was a German revolutionary, sociologist, historian, author and philosopher.
Marx studied law and philosophy at university and he lived in London for many years. His best known work is the Communist Manifesto, the most celebrated pamphlet in the history of the socialist movement.
He collaborated with the German thinker Friedrich Engels, and his writings and theories about society are known as Marxism. He is the author of the theory of class struggle, which is the conflict between the ruling class and the working class.