Graeae
The Graeae, sometimes called the Grey Sisters, are characters from Greek mythology. They are a trio of hags, called Deino, Enyo and Pemphredo.  They are called the Grey Sisters because they were born with grey skin and hair. They also share one tooth and one eye. They take turns using the tooth and eye. The Graeae are affiliated with the gorgons. The hero Perseus made them say where Medusa was by taking their eye. Perseus said he would not give the eye back until the Grey Sisters told him where Medusa was.