According to the International Business Times:
"April Fools’ Day began in the year 1582, according to one legend, when Pope Gregory XIII (after whom the Gregorian calendar is named) moved the start of the new year from the end of March to the beginning of January. The change was made public, but not everyone got the memo, and those who didn’t and thus continued to celebrate New Year's Day on April 1 were laughed at. “Because they were seen as foolish, [they were] called April Fools,”....
Another myth is based on the same idea but suggests the change in the New Year happened at a slightly different time and place. It attributes the calendar change to France in 1564 -- rather than to the pope -- and when people celebrated the wrong New Year, others would paste paper fish on their backs, which explains why in France, the day is known as April Fish."
What are the best April Fools' pranks you have ever heard of/ been a part of/ played on someone? Here's the best one I heard of this year, from none other than The Smithsonian Museum.
Smithsonian displays Wonder Woman's Invisible Jet