Nicolaus Copernicus was a Renaissance-era mathematician and astronomer credited with proposing the heliocentric model of the solar system, where the Sun is at the center and the Earth and other planets orbit around it. His book "De revolutionibus orbium coelestium" (On the Revolutions of the Celestial Spheres) was a groundbreaking work that sparked the Copernican Revolution and revolutionized our understanding of the universe.