The Weird Sisters were a group of three characters in William Shakespeare's Macbeth. (PROSE: The True Tragedie of Macbeth) They were commonly referred to as the three witches. (PROSE: The Empire of Glass, AUDIO: The Carrionite Curse)
Shakespeare based the play on information from Holinshead's Chronicles of England, Scotland and Ireland. He determined Macbeth of Scotland to be a "perfect subject" partly due to the elements of witchcraft in his story. Macbeth was written for King James I and Shakespeare made sure to "pander" to his hatred of witchcraft and his fear of assassination.
The Weird Sisters first appeared in Act I Scene III in which Macbeth (and Banquo) confronted them on the "blasted heath". After this encounter, they vanished, prompting Banquo to ask where they had gone. Macbeth responded magisterially with the words "into the air". (PROSE: The Empire of Glass)
In an early draft of the play, the role of the Weird Sisters was fulfilled by the Doctor, Jamie and Zoe. A version of Macbeth was metafictionally referenced at points of the draft. When the trio disguised themselves as the Weird Sisters in Act IV Scene I, Zoe elected to do most of the talking, leaving the Doctor and Jamie to join in occasionally, because she had "memorised the entire play by heart". (PROSE: The True Tragedie of Macbeth)
The Weird Sisters also featured in The Adventures of Macbeth's Head, a derivative play written by Francis Pearson in 1603, albeit with an additional fourth member. (PROSE: Managra)