Norse mythology

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

When Ace and the Doctor were at Maiden's Point, the Doctor refered to Yggdrasil and the well of Hvergelmir. (DW: The Curse of Fenric)

Behind the scenes

 * The name Fenric is derived from the name of the wolf Fenrir.
 * 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.