May 4 was chosen as Star Wars Day to celebrate George Lucas's Star Wars media franchise because of the pun on the catchphrase "May the Force be with you" as "May the Fourth be with you". The popularity of the day spread quickly via media and fan celebrations even though it was not officially created by Lucasfilm. So Lucasfilm embraced it and the parent company Disney accepted May 4 as an annual celebration of Star Wars.
The first reference of the phrase being used was on May 4, 1979, the day Margaret Thatcher took the oath as the Prime Minister of the United Kingdom. An online news article from a Danish public broadcaster says her political party, the Conservatives, placed a congratulatory advertisement in The London Evening News, saying "May the Fourth Be with You, Maggie. Congratulations."
Some recognize the following day, May 5, as "Revenge of the Fifth", a play on Star Wars: Episode III – Revenge of the Sith and celebrate the Sith Lords and other villainous characters from the Star Wars series rather than the Jedi. Others celebrate this one day later, on May 6, citing "Revenge of the Sixth" as a better play on "Sith", while others refer to the 6th as "Return of the 6th" as a play on the trilogy aspect of the Star Wars films.