Robert Boyle (1627-1691) was one of the first scientists to discuss the concept of primum frigidum, as he called it.
French physicist Guillaume Amontons in 1702 had come very close to deducing the value of absolute zero by extrapolating data from experiments using an air thermometer. Then in the 1780s Jacques Charles made the observation that the volume of a gas at constant pressure increases proportionately as the temperature is increased. This is called Charles' Law, and although Charles didn't publish this result it was magnanimously credited to him by Joseph Louis Gay-Lussac