Fenric

Fenric was an immensely powerful sentient force, at least as old as the Universe itself and an intelligence of pure evil.

Origins
The being later known as Fenric, which has no name, was one of two forces, one good, one evil, which were present at the Dawn of Time. (DW: The Curse of Fenric)


 * The fate of the good force, if personified, remains unknown.

Some sources state that Fenric originated not in the beginnings of this universe but, like the other Old Ones, in a universe before this one. These accounts state that Fenric bore (and still bears) the name of Haster the Unspeakable (NA: All-Consuming Fire).

Entrapment of Fenric
The Doctor's first known encounter with Fenric was in Constantinople in the middle of the 3rd century AD, when the Time Lord challenged the entity to a game of chess, knowing that the metaphorical struggle would weaken Fenric. The ploy worked and the Doctor was able to trap Fenric in a flask and banish him to the Shadow Dimensions. (DW: The Curse of Fenric)

Fenric's stratagem
Yet Fenric's power was such that his influence still continued to pervade space and time, and he began setting into motion the events that would ensure his escape.

Fenric summoned the Ancient One, the last Haemovore, from the future. When Vikings stole the flask containing Fenric sometime after the 10th century, the Haemovore followed them and the flask to Northrumbria and Maiden's Point. Fearing its evil influence, the Vikings buried the flask beneath St. Jude's Church, leaving a runic inscription warning that the flask was cursed. The Haemovore remained beneath the waters of Maiden's Bay, gradually recruiting new members, the Wolves of Fernic, who awaited and their master's release. (DW: The Curse of Fenric)

Meanwhile Fenric continued to manipulate the timelines in ways that would ensure his release. He transported the 17th century [Lady Peinforte]] by time storm during a black magic ritual by Peinforte to travel from 1638 to 1988 to retrieve the Nemesis statue, (DW: Silver Nemesis)

He also created the time storm which engulfed Ace and transported her to Iceworld, where she met the Doctor and joined him on his travels. (DW: Dragonfire) Fenric hoped that he could use Ace as a weapon against the Doctor later. (DW: The Curse of Fenric)

Escape and defeat
In 1943 Fenric finally escaped, killing and occupying first the body of Doctor Judson and then that of Soviet Captain Sorin. He then summoned the Haemovore, whose vampire army arose from the waters and attacked and killed many of the villagers and base personnel at Maiden's Point. The Doctor attempted to trap Fenric once again using a chess game, but by possessing Sorin, Fenric learned the solution to the chess puzzle. Fenric was finally defeated when the Haemovore turned on him, destroying Sorin's body and leaving Fenric without a corporeal host. Fenric's spirit dissipated, although it is likely it's evil influence still persists. (DW: The Curse of Fenric)