Pope Gregory XIII is most famous for establishing the Gregorian calendar, which is the calendar still used today. His papacy also focused on strengthening the Catholic Church's presence in Europe and combating Protestantism. Birth name: Ugo Buoncompagni Nationality: Papal States Born: January 11, 1502 Died: April 10, 1585 Pontificate: June 2, 1572 – April 10, 1585