An Italian astronomer, engineer, and physicist, Galileo Galilei is widely regarded as the father of observational astronomy, the father of the scientific method, the father of modern physics, and the father of modern science. He is credited with popularizing the telescope, which changed the course of history.
Nicolaus Copernicus was a mathematician and astronomer. He is credited with formulating Heliocentrism, which led to the Copernican Revolution. Although Aristarchus of Samos had formulated Heliocentrism 18 centuries earlier, Copernicus was responsible for popularizing it. Copernicus is also credited with formulating an economic principle, which was later called Gresham's law.