Final answer:
Karl Marx is the Prussian (German) social theorist known for his belief that social class is the central element of historical development, focusing on class struggle and the eventual rise of the proletariat against the capitalist class.
Step-by-step explanation:
The Prussian (German) social theorist who viewed social class as the key focus of history is Karl Marx. Marx, a revolutionary philosopher, believed that the history of every society was marked by class struggle. He argued that in industrialized societies, the workers, or the proletariat, would eventually rise up against the ruling capitalist class. Marx proposed that this would lead to an economic and political system that distributed property amongst workers, a theory that formed the basis for modern socialist and communist movements.
Marx's ideas on religion also indicated his focus on social classes. He viewed religion as a tool that reflected and maintained social stratification, perpetuating inequality and the economic suffering of the working class. His famous phrase, "religion is the opium of the people," encapsulates his belief that religion serves as a mechanism for people to numb their socio-economic pain instead of addressing the root causes of their distress.