The custom of setting aside a day, April Fool’s Day, for playing harmless pranks upon one’s neighbor has been relatively common in the world historically.
There are three scenarios regarding the origins of April Fool’s Day.
The day is similar to the Ancient Roman festival Hilaria observed on March 25. The festival was observed to honor the Greek goddess, Cybele. On Hilaria, the Romans indulged themselves with all kinds of games and amusements, most importantly masquerades, where anyone could disguise and imitate anyone they liked.
Another version says the tradition originates with the Celts. Since the Celts were mighty fishermen, the tradition of telling lies on April 1st, is deeply linked to fishing.
The fishing season began on April 1st, but during that period there were not that many fish, therefore leading the fishermen to lie about the amount of fish that they caught. Through time, the tradition remained and expanded in other countries with different versions.