The Great Vampires were massive humanoids from Gallifreyan legend. They came from the Dark Times.
The Great Vampires were colossal humanoids with grey skin and wings. Like lesser vampires, Great Vampires required blood to survive, but due to their large size they needed considerably more. Great Vampires were extremely powerful and one individual could drain a whole planet dry. They had the ability to absorb energy, such as from weapons, and were able to survive numerous minor wounds. The only way to kill one was to stab them through the heart, usually with a iron stake. More powerful Great Vampires needed to have their heart fully destroyed in order to kill them.
The Great Vampires suddenly appeared in the universe, causing mass destruction and chaos. The Great Vampires rampaged through the cosmos during the Dark Times.
Eventually Time Lords hunted these creatures down in a long and bloody war, using bowships to pierce their hearts. Though the Time Lords won, they incurred heavy casualties. Even then, the leader of the Vampires escaped into the smaller universe of E-Space. After time, the records of this war were lost and passed into legend, but every Time Lord, even to the Doctor's time had a solemn directive to kill any Great Vampire they might find.
Great Vampires created the Vampires from Earth. They may be one and the same as the Yssgaroth.