The "Weird Sisters" aka "The Three Witches" in Shakespeare's Macbeth play a pivotal role- it is they who plant the seed that stirs Macbeth's ambition and "tempts" him to plot to murder the king.
But "weird" is not the same "weird" we use today. Most critics believe these 3 are related to the Greek "3 Fates" or the "Norns" of of Norse mythology (in ancient Scotland known as "Wyrd"). You can read all about that here.
You might have even spotted them in Walt Disney's "Sleeping Beauty"!
And what about Harry Potter? This excerpt is from Wikipedia:
J. K. Rowling has cited the Three Witches as an influence in her Harry Potter series. In an interview with The Leaky Cauldron and MuggleNet, when asked, "What if [Voldemort] never heard the prophecy?", she said, "It's the 'Macbeth' idea. I absolutely adore 'Macbeth.' It is possibly my favourite Shakespeare play. And that's the question isn't it? If Macbeth hadn't met the witches, would he have killed Duncan? Would any of it have happened? Is it fated or did he make it happen? I believe he made it happen."[33] On her website, she referred to Macbeth again in discussing the prophecy: "the prophecy (like the one the witches make to Macbeth, if anyone has read the play of the same name) becomes the catalyst for a situation that would never have occurred if it had not been made."[34] More playfully, Rowling also invented a musical band popular in the Wizarding world called The Weird Sisters that appears in passing in several books in the series as well as the film adaptation of Harry Potter and the Goblet of Fire. The third Harry Potter movie's soundtrack features a song by John Williams called "Double Trouble", a reference to the witches' line, "Double double, toil and trouble". The lyrics of the song were adapted from the Three Witches' spell in the play.
