The Three Fates are all female immortals who predict the destiny and fate of mortals, gods and demigods. Even the greatest powers, like the Titans could not cheat fate.
The Fates have awesome power, of deciding ones destiny. They decide if a man is good or evil, depending on what should happen. The most obvious choice, is how long this person will live. There are three Fates, Clotho, the spinner who spins the thread of life. Lachesis, the one who measures the thread, who chooses the lot in life one will have and measures how long their life should last. Atropos she who cannot be turned, who at death with her scissors snips the thread of life, causing someone to die, soon, or presently. Percy Jackson once described them as "creepy old ladies," in The Lightning Theif.
The Fates are described as old women, who predate the gods. It is not mentioned, or clear how far their power extends, but they predict the fate of the gods, Titans, Earthborn etc. In any case, not even the most powerful is willing to talk back to the Fates, or try to fight them.
There were different fates for both Greek, and Roman mythology. The Roman fates were called Parace, and the Greek fates were called Moirai. The fates were referred to as "the white robed incarnations. Or more generously, the "sparing ones."