Sirleto, Guglielmo, a learned Italian, was born in 1514 at Guardavalle, near Stiro, in Calabria, of a poor but honorable family, and was early destined to the Church. His intelligence and prodigious memory enabled him to make remarkable progress in study, and he soon gained influential friends, who at length procured him the position of librarian of the Vatican in 1549. Successive popes added to his honors and emoluments, including the cardinalate (1565), and the bishopric of San Marco in Calabria (1566), then that of Squillaci (1568), which he resigned in 1573, to devote himself wholly to the Vatican library. He died at Rome, Oct. 8, 1585, leaving some religious works, which are enumerated in Hoefer, Nouv. Biog. Generale, s.v.