The day for pranks, jokes and hoaxes A look back at some of the most famous April Fool’s Day jokes. By John M. CowanApril 1, 2009 SHARE The origins of April Fool’s Day are, fittingly, a bit of a mystery. Some say it began after the adoption of the Gregorian Calendar in the 16th Century, as a derogatory term for people still clinging to the outmoded Julian Calendar. To read the full story, log in. Become a Ragan Insider member to read this article and all other archived content. Sign up today Already a member? Log in here. Learn more about Ragan Insider.