Natural son of Gregory XIII (1502-1585, Pope from 1572), Jacopo (or Giacomo) Boncompagni was appointed by his father keeper of the Castel Sant'Angelo and commander of the pontifical troops. Legitimated in 1576, he acquired, among other possessions, the Duchy of Sora, where he retired after his father's death. A student of the humanities and the sciences, he was known as a generous patron of the arts.