If you’re on social media you’ve probably seen at least one of your friends posting a “May the Fourth Be With You!” status or meme.  It’s a great pun that rolls around once a year on Star Wars Day, and it’s followed by Revenge of the Fifth (aka, “Sith Day”) and Return of the Sixth.

Like most memes, it’s easy to dismiss this joke as having arisen organically out of nothing.  But like most memes, it actually has a surprisingly dense history.  Let’s dive in!

The first thing you should know is that Star Wars first came out on May 25, 1977.  (“Episode IV: A New Hope” was originally simply titled “Star Wars.”)

The first recorded instance of the “May the Fourth!” phrase occurred only two years later, on May 4th, 1979, when a paid ad in The London Evening News appeared to congratulate Margaret Thatcher on becoming prime minister.  “May the Fourth be with you, Maggie!  Congratulations!” read the ad, run by the Conservative party.

Following this instance, there are plenty of examples of the phrase being passed around, mostly by word of mouth, particularly in the United Kingdom, where multiple politicians and members of Parliament seemed to enjoy the joke.  (The Prime Minister typically takes office on May 4th.  Boris Johnson’s 2012 acceptance speech also included the phrase “May the Fourth Be With You.”)

Social media gave the phrase a wider range, lending itself to more celebrations.  Called “Luke Skywalker Day” by some and simply “Star Wars Day” by others, in 2011 it gained enough traction to lend itself to an organized celebration in Toronto by the Toronto Underground Cinema, complete with a couple of hashtags: #MayThe4thBeWithYou and #StarWarsDay.  The event’s reception was warm, and the attendance large enough to justify a second production the next year.

In October of 2012, LucasFilms was acquired by Disney, who immediately understood the marketing potential of May the Fourth as “Star Wars Day.”  On May 4th, 2013, just seven months after Disney bought LucasFilms, they hosted a May The Fourth event complete with exclusive merchandise, making May the Fourth an “official” holiday.  If you head over to the Star Wars website, there’s a whole page dedicated to this pun, including sales deals, events, games, activities, and more.

Aside from the obvious appeal of the pun, May 4th is also, sometimes, Free Comic Book Day, a Marvel promotion which occurs on the first Saturday of May, giving it an easy marketing tie-in for comic book shops to push Star Wars graphic novels.

Curiously, for a long time, May the Fourth was not recognized as “Star Wars Day” because LucasFilms insisted that “Star Wars Day” was May 25th, the anniversary of the premiere of the first movie.  May 25th carries a lot of weight among geeks.  Not only is it the anniversary of Star Wars, but it’s also Geek Pride Day, begun in the late ‘00s.

May 25th is also a significant day in several other geek fandoms.  The Glorious Twenty-fifth of May is a celebration recognized by the survivors of the People’s Revolution on Terry Prachett’s Discworld, who recognize it by wearing sprigs of lilac.  It’s also Towel Day, a tip of the hat to Douglas Adams’ The Hitchhiker’s Guide to the Galaxy, which fans celebrate by carrying a towel around with them, as per the advice of the Hitchhiker’s Guide.

Adding to the confusion, the Los Angeles City Council officially declared May 25th as Star Wars Day in 2007, on the 30th anniversary of Star Wars.

But the appeal of the “May the Fourth” pun was too strong, although LucasFilms continued to insist, up until its acquisition, that May 25th was Star Wars Day.  Once Disney took the helm, they trademarked Star Wars Day and officially declared it to be May 4th, not May 25th.  Since 2013, Disney has had Star Wars Day events at Disneyland and Disney World, celebrating Star Wars Day on May 4th.

And in 2015, astronauts aboard the International Space Station watched Star Wars on the 4th, ensuring the pun’s place in history.