Claudius Ptolemy was a Greco-Roman mathematician, astronomer, geographer, and astrologer active in Alexandria during the 2nd century CE. His recorded astronomical observations date from 127 to 141 CE, placing his career under the reign of Antoninus Pius. Ptolemy synthesized earlier Greek, Babylonian, and possibly Egyptian knowledge, most notably building upon the astronomical models of Hipparchus.

Though details of his personal life are scarce, his prolific output indicates he worked within Alexandria’s scholarly community, dedicating some works to a figure named Syrus. Ptolemy’s major surviving works in Greek include the Almagest, a comprehensive astronomical treatise; the Geography; the astrological Tetrabiblos; the Harmonics; the Optics; and several specialized texts like On the Analemma and the Planetary Hypotheses.

His significance lies in his systematic compilation and mathematical refinement of ancient science, which remained authoritative for over a millennium. The geocentric model in the Almagest dominated astronomy until Copernicus, while his Geography fundamentally shaped medieval and Renaissance cartography.