Norse mythology

Norse mythology was the mythology of a pre-Christian pagan religion of the Vikings in Scandinavia (Norway, Iceland, Sweden and Denmark).

Gods and other beings
Odin was the mythical king of the gods. He had only one eye and wore an eyepatch. When the Mire arrived in a Viking village, their leader took Odin's form based on the beliefs of the Vikings in the town. (TV: The Girl Who Died) Odin was the father of Thor. (PROSE: The Spear of Destiny)

Sleipnir was an eight-legged horse from Norse mythology. In 1006, the Norse King Sitric Silkbeard of Dublin named his own horse after the legendary animal. (AUDIO: The Book of Kells)

Loki was known as a mischievous god of many faces and a trickster. The Doctor was accidentally responsible for the creation of the Loki legend, which came back to haunt him when he was identified as Loki by a Viking princess. (PROSE: Dark Horizons)

Cosmology
Jötunnheim was one of the nine worlds in Norse mythology, inhabited by the Jötunn, or frost giants. (AUDIO: Shield of the Jötunn)

Parts of Norse mythology included the great ash tree Yggdrasil, Hvergelmir, a well of poison (which turned out to be a natural well of poisons located at Maiden's Point) and the Great Serpent, prophesied to rise from the sea and spew venom over all the Earth. Fenric took advantage of these myths, planning to have the Great Serpent Ingiger take the poison from Maiden's Point and carry it to the sea to poison the world forever. Fenric's name, though not his real one, and his "wolves" were also based on the Ragnarok myth. (TV: The Curse of Fenric)

Cultural references
The Garm guarded the Forbidden Zone on Terminus, working in part with the Vanir. (TV: Terminus)

The artificial intelligence WOTAN (Vo-tan) shared its name with the High German god Wotan, who corresponded with the Norse god Odin. (TV: The War Machines)

Anthony Rupert Hemmings believed that the Timewyrm was one of the Norse gods. (PROSE: Timewyrm: Revelation)

While crossing a stream of mercury, the Seventh Doctor compared it to Elivâger, the stream that flowed through Ginnunga Gap. (PROSE: Cat's Cradle: Time's Crucible)

In the early 21st century, several new types of United Nations aircraft and weapons were named after Norse gods, such as the Odin (a remote-controlled helicopter) and the Loki (a fighter plane armed with Valkyries, Niffelheims and Ragnaroks). (PROSE: Cat's Cradle: Warhead)

Tiw Heimdall compared the Bridge, a trisilicate filament linking the moons Belial and Moloch, to Bifrost, the rainbow bridge of the Aesir in Norse mythology. (PROSE: Lucifer Rising)

Behind the scenes

 * The name Fenric is derived from the name of the wolf.
 * The Gods of Ragnarok's name is from the Nordic Ragnarök, which is often misunderstood as the "End of the World" or Armageddon. While an important part of Ragnarök is a climactic and cataclysmic battle, it ultimately ends with the renewal of the world as new and fertile.
 * One translation of Ragnarök is "the End of the Gods"; thus; the Gods of Ragnarok are "the Gods of the End of the Gods". This could be interpreted either as an added layer of meaning, or as nonsense.