Theon (c. 335 - c. 405 AD) was a scholar and the last director of the Library of Alexandria in the Museion, until it was demolished by the patriarch Theophilus on order of the emperor Theodosius in 391 AD. He wrote some commentaries on important works by his hellenistic predecessors, notably the Almagest and the "Handy Tables" by Ptolemy. Apparently he is the first author on the theory of "trepidation of the equinoxes", as an alternative to precession.
Theon was the father of Hypatia. Perhaps his most lasting achievement was his edition of EuclidsElements which was published in ~364. This edition remained in publication in some form until 1814 or an astonishing ~1450 years.
