Pythia

The Pythia was a name as much as a title.

The Pythia was the leader of Gallifrey prior to Rassilon, she ruled as part of a matriarchy, she ruled because she had powerful psychic powers, and could see the future. (NA: Cat's Cradle: Time's Crucible)

The Pythia ruled a Gallifrey which was government by mystery and superstition.

The 389th Pythia gave the Legendary Hero Ao a jewled periapt with a tongue of blue ice. (NA: Cat's Cradle: Time's Crucible)

Pythia's Curse
Near the end of her reign as Pythia the last Pythia was unable to see into the future, in an attempt to see further she recruited Vael (a skilled Gallifreyan with psychic-powers) to work with her and then spy on Rassilon.

When her idea of her future failed to come she send her followers to Karn and then cursed Gallifrey with sterility and threw herself into an abyss below her temple. (NA: Cat's Cradle: Time's Crucible)

Remnants of the Pythia
The Pythia's followers fled to the planet Karn where they eventually became the Sisterhood of Karn.