The Three Witches or Weird Sisters; "the Fates"

"The Three Witches or Weird Sisters are characters in William Shakespeare's play Macbeth (c. 1603–1607). Their origin lies in Holinshed's Chronicles (1587), a history of England, Scotland and Ireland. Other possible sources influencing their creation aside from Shakespeare's own imagination include British folklore, contemporary treatises on witchcraft including King James I and VI's Daemonologie, Scandinavian legends of the Norns, and ancient classical myths concerning the Fates, the Greek myths of the Moirai and the Roman myths of the Parcae. Portions of Thomas Middleton's play The Witch were incorporated into Macbeth around 1618.

Shakespeare's witches are prophets who hail the general Macbeth early in the play with predictions of his rise as king. Upon committing regicide and taking the throne of Scotland, Macbeth hears the trio deliver ambiguous prophecies threatening his downfall. The witches' dark and contradictory natures, their "filthy" trappings and activities, as well as their interaction with the supernatural all set an ominous tone for the play.

In the eighteenth century the witches were portrayed in a variety of ways by artists such as Henry Fuseli. Since then, their role has proven somewhat difficult for many directors to portray, due to the tendency to make their parts exaggerated or overly sensational.

Some have adapted the original Macbeth into different cultures, as in Orson Welles's performance making the witches voodoo priestesses. Film adaptations have seen the witches transformed into characters familiar to the modern world, such as hippies on drugs or goth schoolgirls. Their influence reaches the literary realm as well in such works as The Third Witch and the Harry Potter series."

Source
http://en.wikipedia.org/wiki/Three_Witches