https://www.vice.com/en_us/article/5d9p3q/april-fools-day-deepfakes-pope-trump-arrest-gpt

The true origin of April Fool’s Day is not only a mystery today—it’s considered unknowable.

Historians have their theories about how the centuries-old holiday started: Most likely, it was something about the moveable timing of Easter, or the trickiness of spring weather, or an inside joke among 16th century people about the date of the new year. We still celebrate April Fool’s today without knowing why or what it means. It’s a deep-fried meme of a holiday.