Gregory XIII, pope of the Catholic Church (born 1502)

Pope Gregory XIII was head of the Catholic Church and ruler of the Papal States from 13 May 1572 to his death in April 1585. He is best known for commissioning and being the namesake for the Gregorian calendar, which remains the internationally accepted civil calendar to this day.

April 10 is the 100th day of the year in the Gregorian calendar; 265 days remain until the end of the year.