Who devised the calendar?

The modern calendar system, known as the Gregorian calendar, was devised by Pope Gregory XIII in 1582. It was created to correct inaccuracies in the Julian calendar, which had been in use since 45 BCE. The Gregorian calendar introduced a more precise method of calculating leap years to better align the calendar year with the solar year. Various cultures and civilizations throughout history have also developed their own calendars, such as the Maya and the Islamic calendar.