Who invented April Fools' Day?

Then in 1562, Pope Gregory introduced a new calendar for the Christian world, and the new year fell on January first. There were some people, however, who hadn't heard or didn't believe the change in the date, so they continued to celebrate New Year's Day on April first. Others played tricks on them and called them "April fools." They sent them on a "fool's errand" or tried to make them believe that something false was true.