Today is Star Wars Day when fans all over the world celebrate the long running science fiction franchise. The date was chosen as "May the Fourth be with you" is a  pun on the quote "May the Force be with you".

It's not known where in Star Wars fandom it originated but the first recorded reference of the phrase being used was when Margaret Thatcher become UK Prime Minister on 4th May 1979 and the London Evening News printed a congratulatory advert saying  "May the Fourth be with you". 

Today Lucasfilm and their parent company Disney acknowledge it as a day of celebration along with many millions around the world.