Rudolf Clausius
German physicist commonly known as one of the founders of thermodynamics. The notion of entropy is usually attributed to him, but many of his papers are often obscure or confusing. According to Edward Daub and others, Clausius derived some of the essential ideas from Reech and Rankine. And the concept of entropy was not established until 1865. Clausius is also responsible for some of the basic ideas for the kinetic theory of gases.