Lord Kelvin

William Thomson, 1st Baron Kelvin (26 June 1824 - 17 December 1907) Among many things, Lord Kelvin is associated with the creation of the First and Second Laws of Thermodynamics and the temperature scale of Kelvin.

His work on the Laws of Thermodynamics began after hearing another attempt made by James Prescott Joule to discredit the highly popular caloric theory associated with heat. Unlike many of the attendees, Kelvin was intrigued enough to listen to Joule's work, even though he himself was skeptical. Kelvin still believed the Carnot–Clapeyron caloric theory, however, he began to doubt it after experiments he performed himself. The caloric theory did not yield an "absolute temperature scale", only an "operational definition of temperature".

References https://en.wikipedia.org/wiki/William_Thomson%2C_1st_Baron_Kelvin