Sibyl

Sibyl started a soothsaying cult in Pompeii (DW: The Fires of Pompeii)

It is unknown why Sibyl started the cult or what She used it for but the Doctor stated that she ran the cult less violentley while She lived. The Doctor has said to have had a brief relationship with the Sibyl, but the Doctor thought that it wouldn't work (which she had prophesied already).