Papa Grigore al XIII-lea

Pope Gregory XIII, who reigned from 1572 to 1585, is best known for instituting the Gregorian calendar, which corrected inaccuracies in the Julian calendar. His decision to reform the calendar was driven by the need to realign the timing of important religious dates, particularly Easter, with the solar year. The Gregorian calendar has since become the most widely used civil calendar in the world today.