First Baron Kelvin, also known as William Thomson, was a prominent physicist and mathematician in the 19th century. He is best known for his work in thermodynamics and the development of the Kelvin scale for temperature measurement. Though he is most commonly referred to as "First Baron Kelvin," there are several synonyms that may be used to describe him. These include "William Thomson, 1st Baron Kelvin," "Sir William Thomson," and "Lord Kelvin." Each of these titles refers to the same individual, who made significant contributions to the fields of science and mathematics during his lifetime.