1. No definitive history is known for the date, but several theories exist to explain the origin of April Fools' Day. One cites 1582, when Pope Gregory XIII called for his followers to adopt a new calendar (which became known as the Gregorian calendar) calling January 1 the first day of the year. This replaced the Julian calendar, which cited April 1 as the first day. People who either refused to accept the new calendar or didn't know it existed were ridiculed as April Fools.

6. Famous Pranks: Google has been known to trick its users on April Fools' by announcing bogus new features such as the MentalPlex which would read a user's mind to determine what he wanted to search for. It has also posted job listings for its planned research center on the moon, and unveiled the Google Gulp, a new drink that would work in conjunction with Google searches, activating the brain's neurotransmitters to make the user/drinker more intelligent.