Final answer:
The Gregorian Calendar is based on the birth of Christ and was established by a Christian monk named Dionysius Exiguus. It is named after Pope Gregory XIII and is one of the most widely used calendars in the world.
Step-by-step explanation:
The Gregorian Calendar is based on the birth of Christ.
In the 6th century, a Christian monk named Dionysius Exiguus established the reference date for the year zero in Europe based on the tenets of Christianity. This calendar system, which uses the designations Anno Domino (AD) and Before Christ (BC), was adopted by the early Christian Church and eventually became the foundation for the Gregorian Calendar.
It should be noted that various cultures and religions also developed their calendars, but the Gregorian Calendar, which is named after Pope Gregory XIII, stands as one of the most widely used calendars today.