Final answer:
Karl Marx called religion the "opium of the people," viewing it as a tool used to soothe and maintain the inequality and social stratification in society.
Step-by-step explanation:
The person who called religion the "opium of the people" was Karl Marx. German philosopher, journalist, and revolutionary socialist Karl Marx was deeply interested in the social impact of religion.
According to Marx, religion serves to maintain inequality and perpetuates the status quo, particularly by reflecting the social stratification of society. He believed that religion is a means of soothing the economic suffering of the working class, thus he famously described it as the opium of the people in his writings in 1844.
Marx's critique of religion was part of his broader theory on society and economics, in which he saw the history of society largely as a struggle between social classes.