Tisiphone is one of the three Fury Sisters. She is sister to Megaera and Alecto.
After Megaera has been defeated a certain number of times, Alecto and Tisiphone will begin appearing, randomly substituting her in Tartarus. Tisiphone does not appear in the House of Hades after she's been defeated.
'...Among each of the deathless Fury Sisters, the one known as Tisiphone is probably responsible for the particularly fearsome reputation they all share, both on the surface of the earth and here below. This is of course not to diminish the deserved notoriety that they each, in turn, have earned through their efficient torturing of those who tried to get away with terrible misdeeds in life; and yet, Tisiphone, among the three, least shares the qualities with which mortals can identify. What could have caused Tisiphone to focus so relentlessly upon her task of punishing murder? She is unlikely to ever say, although the tales of the Furies having come from the spilt blood of the eldest of the Titans offers fertile ground for speculation on the matter.'