Rudolf Julius Emanuel Clausius (January 2, 1822 –August 24,1888) is a German physicist and mathematician and is considered one of the central founders of the science of thermodynamics.

By his restatement of Sadi Carnot's principle known as the Carnot cycle, he gives the theory of heat a truer and sounder basis.

His most important paper, "On the Moving Force of Heat", published in 1850, first states the basic ideas of the second law of thermodynamics.

In 1865 he introduces the concept of entropy

In 1870 he introduced the virial theorem, which applies to heat.