May 4 is Star Wars Day. Fans of the franchise greet each other with "May the Fourth be with you" all day in a nod to the classic movie line, "May the force be with you." The holiday has grassroots origins, thanks to the Internet allowing fans to unite and connect with each other.
According to starwars.com, the earliest reference to May 4 actually comes from 1979, when author Alan Arnold was chronicling the making of the second film in the franchise (but, in order of the storyline, film 5), The Empire Strikes Back.
Arnold wrote on May 4, 1979, "Margaret Thatcher has won the election and become Britain's first woman prime minister. To celebrate their victory her party took a half page of advertising space in the London Evening News. This message, referring to the day of victory, was 'May the Fourth Be With You, Maggie. Congratulations,' further proof of the extent to which Star Wars has influenced us all."