Theon of Alexandria was a Greek mathematician and astronomer of the 4th century CE, active in Alexandria during the reigns of Theodosius I and Arcadius. He held a position at the Museum, Alexandria's institution of higher learning, and is noted as its last attested member. He is most widely remembered as the father and teacher of the philosopher Hypatia.

His scholarly output consisted of influential commentaries and editions of foundational texts. Theon produced the standard commentary on Ptolemy's Almagest and a definitive edition of Euclid's Elements, which included his own notes and alternative proofs. He also wrote a commentary on Ptolemy's Handy Tables and a treatise on the astrolabe.

Theon played a crucial role in preserving and transmitting classical Greek mathematics and astronomy. His editions, which incorporated corrections and updates, became essential textbooks for Byzantine, Islamic, and later scholars. He serves as a vital link between antiquity and the medieval period, both through his widely circulated works and through his famous daughter, Hypatia.