Constantin Carathéodory (or Constantine Karatheodori) (Greek: Κωνσταντίνος Καραθεοδωρή) (September 13, 1873 – February 2, 1950) was a Greek mathematician. He made significant contributions to the theory of functions of a real variable, the calculus of variations, and measure theory. His work also includes important results in conformal representations and in the theory of boundary correspondence. In 1909, Carathéodory pioneered the Axiomatic Formulation of Thermodynamics along a purely geometrical approach.