The Ancient One (The Curse of Fenric)

The Ancient One was one of last of the original Haemovores. It lived on a polluted Earth, after all of its children had died from the pollution.

Biography
It was then brought to 10th century Transylvania by Fenric. Fenric commanded him to follow the vikings who had stolen the flask containing Fenric. It fed on them, turning many of them into Haemovores. It and the Haeamovores followed the vikings and after they were killed by the pirate Hemming, following him to Maiden's Bay. Though Hemming and all his men were killed by the Ancient One, Hemming had buried the flask beneath St. Jude's Church where they could not get it.

Eventually, in 1943, the Ancient One was awakened again by Fenric. It was used to control the Haemovores, which were used to attack the soliders in the base. Using the poisons made by the nearby base, Fenric intended to pollute the world, causing the future that created the Haemovores. The Doctor was able to convince Ingiger to betray Fenric, convincing it that Fenric would not return him to his own time. The Ancient One killed both itself and Fenric by going into the isolation chamber with Fenric and releasing a poison. (DW: The Curse of Fenric)

Behind the scenes
The novelisation of The Curse of Fenric names the Ancient One 'Ingiger' and gives its gender as female, despite being portrayed by a male actor.