Great Vampire

The Great Vampires were gigantic humanoids in Gallifreyan legend that lived during the Dark Times.

Biology
The Great Vampires were colossal humanoids with grey skin and wings. Like lesser vampires, Great Vampires needed blood to survive, but their large size dictated they needed considerably more. Great Vampires were extremely powerful and one individual could drain a whole planet dry. They could absorb energy in almost any form and survive numerous minor wounds. The only way to kill one was to stab them through the heart, usually with a steel bolt. More powerful Great Vampires needed to have their heart fully destroyed in order to kill them. (TV: State of Decay)

Their appearance could cause hallucinations, in which they could appear as horrible, huge, winged snakes with many eyes. (PROSE: The Pit)

Reign
The Great Vampires suddenly appeared in the universe, causing mass destruction and chaos, (TV: State of Decay) having been accidentally released from their dimension into the universe by the Time Lords. (AUDIO: Project: Twilight)

According to a transmission which Samantha Jones received on Anathema, the Great Vampires originated from another plane of existence, and gained entry into our universe when, during Rassilon's first attempt to harness the power of a black hole, he punched a hole into their universe. However, this transmission may have been influenced by Faction Paradox propaganda. (PROSE: Interference - Book One)

The Great Vampires rampaged through the cosmos during the Dark Times, (TV: The Infinite Quest) and eventually created the Vampires on Earth. (PROSE: Vampire Science)

War with the Time Lords
Eventually Time Lords, led by Kopyion Liall a Mahejetsu, (PROSE: The Pit) hunted these creatures down in the long and bloody war, using bowships firing mighty bolts of steel to pierce their hearts. (TV: State of Decay) The war lasted for a thousand years and saw star systems destroyed and billions killed. Though the Time Lords were eventually able to push the Great Vampires back to their own universe, their King Vampire escaped into the smaller portion of E-Space, and the Great Vampires would later again try to get back into the normal universe. (PROSE: The Pit)

Over time, records of this war were lost and passed into legend. Rassilon, who held the title "Conqueror of Yssgaroth", (AUDIO: Zagreus) wrote data about the vampires that was installed into every Type 40 time vessel. It said that the King Vampire had vanished and it was a Time Lord's solemn duty to lay down his life to kill it. In reality, this King had escaped into the smaller universe of E-Space. This war was said to have sickened Time Lords of violence forever. (TV: State of Decay)

The King Vampire
The King Vampire fell into E-Space, using his great power to draw the ship Hydrax with him. He turned the people on this ship, three humans, into vampires. They fed and served him for a thousand years until the Time of Arising. As he rose from the ground the Fourth Doctor used a Scout ship from the Hydrax to pierce his heart, killing him. (TV: State of Decay)

An alternate perspective
During the events involving the Eighth Doctor's infection with anti-time, the TARDIS constructed a holographic projection of events from the Gallifreyan Time of Chaos.

In this projection, a group of Gallifreyans investigated Rassilon's work on regeneration, time travel, and other projects. The prime investigator was the head of the Arcalian Chapter Houses, Provost Lord Tepesh. In the projection, Tepesh revealed himself as a Great Vampire in disguise, even saying he was a direct descendant of the King Vampire.

Tepesh claimed the Great Vampires were a peaceful lot, content to drink the blood of non-sentient, genetically bred cattle, until Rassilon showed up and declared the Vampires should not be allowed to exist. The subsequent 500-year war was more one of extermination than titanic conflict. (AUDIO: Zagreus)

Alternate timeline
During one of Romana II's, Leela's and Narvin's trips to Alternative Gallifreys they visited one where Rassilon, after completing the Transduction barrier, was killed by the Great Vampires, who then darkened the barrier to block out all light so they might live safely on Gallifrey. Over the next couple of millennia the vampires gradually took over the True Lords, until the battle between the vampire Lord Prydon and the True Lady Magestrix Borusa. During this battle, with the help of Leela (her sight restored after drinking vampire blood), Narvin and Romana helped Borusa and recaptured the Transduction barrier, increasing the light levels allowed to pass through and destroying the Vampires. However, this made Romana feel like she was becoming a "Destroyer of Worlds" as according to her she had killed the Vampires and the Time Lords of her universe. (AUDIO: Annihilation)

Behind the scenes
According to the invalid source Doctor Who: Creatures and Demons, the Plasmavores are believed to be descended from the Great Vampires.

External link
Yssgaroth