Gugliemo Sirleto

Guglielmo Sirleto (* 1514 in Guardavalle in Calabria; † October 6, 1585 in Rome ) was a Cardinal of the Catholic Church.

He first belonged to the Roman Curia, and was Bishop of San Marco Argentano, later of Squillace. He was appointed on 12 March 1565 by Pope Pius IV to the cardinal. He was involved in the drafting of the Roman Catechism, as the Roman Breviary and Missal. He was responsible for the drafting of a new Roman martyrology. He was also chairman of the commission for the reform of the calendar under Gregory XIII.

1554 he was appointed curator of the Vatican Library. In 1572 he became Cardinal Librarian, 1573 Member of the newly formed Reform Congregation for the Greeks. On November 1, 1579, he was named Gregory XIII. with the bull Benedictus Dominus protector for the newly formed Basilianerkongregation that had held on Pentecost in 1579 on the orders Sirletos their first general chapter.

His tomb is in the church of San Bernardino da Siena.