The first person to propose the theory of heliocentrism was the ancient Greek philosopher and mathematician Aristarchus of Samos, who lived around the 3rd century BCE. However, it was Nicolaus Copernicus, in the 16th century, who formally established and popularized the heliocentric model. In his work "De revolutionibus orbium coelestium," published in 1543, Copernicus argued that the Earth and other planets orbit the Sun, which challenged the long-accepted geocentric model advocated by Ptolemy. Copernicus' ideas laid the groundwork for modern astronomy and sparked a scientific revolution, influencing notable figures such as Galileo Galilei and Johannes Kepler.