Copernicus placed the Sun at the center of the universe in his heliocentric model. More precisely, he placed the Sun near the center of the planetary system and argued that Earth was a moving planet rather than the fixed center of creation.
Nicolaus Copernicus outlined this revolutionary arrangement in the early 1500s and published it in De revolutionibus orbium coelestium in 1543, the year of his death. Earth, in his system, rotated daily and revolved around the Sun annually. This explained the apparent daily movement of the sky and the apparent backward, or retrograde, motion of planets without requiring Earth to remain stationary.
Copernicus did not create the first Sun-centered theory: the ancient Greek astronomer Aristarchus of Samos had proposed a similar idea centuries earlier. Copernicus also retained circular orbits and epicycles, so his model was not identical to modern astronomy. Later, Kepler showed that planetary orbits are ellipses, and Newton explained their motion through gravity.