Pope Gregory XIII, born Ugo Boncompagni in 1502, served as the head of the Roman Catholic Church from 1572 until his death in 1585. He is best known for instituting the Gregorian calendar, which corrected inaccuracies in the previous Julian calendar. This reform was essential for aligning the calendar with the solar year and the timing of important Christian holidays. During his papacy, Gregory XIII also focused on strengthening the Catholic Church's influence through the Counter-Reformation. He supported the establishment of new religious orders, such as the Jesuits, and promoted education and missionary work to counter the spread of Protestantism.