Ptolemy was an ancient Greek astronomer, mathematician, and geographer who lived in Alexandria, Egypt, during the 2nd century AD. He is best known for his work, the Almagest, which presented a geocentric model of the universe, placing the Earth at the center and describing the movements of celestial bodies. In addition to his astronomical contributions, Ptolemy wrote the Geographia, a comprehensive guide to the geography of the known world. This work included maps and coordinates, influencing cartography for centuries. His ideas remained dominant until the Copernican revolution in the 16th century, which introduced a heliocentric model of the solar system.