Not a lot is known about the Fates. They are three sisters, but only one appears at a time. One sister is a beautiful little girl, the other is a plain middle-aged woman, and the third is an old woman. Eve Levine made an deal with them to get Lucas Cortez and Paige Winterbourne out of the afterlife. The fates collect on this promise in Haunted. They enforce the afterlife rules such as necromancers aren't allow to contact their dead relatives.
The Fates may be originated from a old greek legend of the three Moirae, telling of three sisters who, wove the thread of a person's life, chose how long they lived and cut the thread of life, ending the person's life.