Karl Heinrich Marx (5 May 1818 - 14 March 1883) was a German philosopher, historian and social theorist famous for his form of political communism referred to as Marxism. Marx also wrote on religion, valuing a reductionist approach and remaining highly critical of the beliefs, with a generally negative view of the social implications of religious institutions. Marx's arguments against religion are highly controversial.
- "Religion is the sigh of the oppressed creature, the heart of a heartless world and the soul of soulless conditions. It is the opium of the people. The abolition of religion as the illusory happiness of the people is the demand for their real happiness. To call on them to give up their illusions about their condition is to call on them to give up a condition that requires illusions."