Nicolaus Copernicus was a Polish astronomer who lived during the Renaissance. He is best known for proposing the heliocentric model of the universe, which suggests that the Earth and other planets revolve around the Sun. This idea was revolutionary at the time, challenging the long-held belief that the Earth was the center of the universe. Copernicus published his groundbreaking work, "De revolutionibus orbium coelestium," in 1543. His theories laid the foundation for modern astronomy and influenced later scientists like Galileo Galilei and Johannes Kepler. Copernicus's ideas helped shift our understanding of the cosmos and marked the beginning of the Scientific Revolution.