Don Diogo Ortiz de Vilhegas, in Spanish Diego Ortiz de Calzadilla or Villegas (died 1519), was a Castilian priest, theologian and astronomer at the service of the Portuguese monarchs.
During his rule, he led a comprehensive artistic remodelling of Viseu Cathedral.
Ortiz advised the Portuguese kings on matters related to astronomy and navigation during the Age of Discovery.
Manuel I named him tutor of his heir, future John III of Portugal.
Ortiz taught on the writings of Cato, Terence, Virgil, Sallust and some parts of the Bible, the theory of the planets and some elementary matters about astrology he heard from Tomás de Torres, an eminent doctor and astrologer of that time.