Pope Gregory XIII- He was born January 7, 1502 and died April 10, 1585. He is best known for creating the Gregorian calendar, which is the calendar still in use in the West today. According to the Julian calendar, the year is 365 days. So, in 1582 Gregory simply "deleted" 10 days from the new calendar, which now included "leap days" in order to make up for more accumulated time in the future.

Source: http://atheism.about.com/library/glossary

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