Ptolemy was an ancient Greek mathematician, astronomer, 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. This model dominated Western astronomy for over a thousand years. In addition to the Almagest, Ptolemy wrote the Geographia, which compiled knowledge of the world's geography and introduced a system of latitude and longitude. His contributions laid the groundwork for future explorations and map-making, influencing both science and navigation.