In Norse mythology, Garmr or Garm (Old Norse "rag") is a wolf or dog associated with both Hel and Ragnarök, and described as a blood-stained guardian of Hel's gate.
The Poetic Edda poem Grímnismál mentions Garmr:
The best of trees | must Yggdrasil be,
Skíðblaðnir best of boats;
Of all the gods | is Óðinn the greatest,
And Sleipnir the best of steeds;
Bifröst of bridges, | Bragi of skalds,
Hábrók of hawks, | and Garm of hounds.
One of the refrains of Völuspá uses Garmr's howling to herald the coming of Ragnarök:
Now Garm howls loud | before Gnipahellir,
The fetters will burst, | and the wolf run free;
Much do I know, | and more can see
Of the fate of the gods, | the mighty in fight.
After the first occurrence of this refrain the Fimbulvetr is related; the second occurrence is succeeded by the invasion of Jötnar (giants) in the world of gods; after the last occurrence, the rise of a new and better world is described.
Baldrs draumar describes a journey which Odin makes to Hel. Along the way he meets a dog.
Then Óðinn rose, | the enchanter old,
And the saddle he laid | on Sleipnir's back;
Thence rode he down | to Niflhel deep,
And the hound he met | that came from hell.
Bloody he was | on his breast before,
At the father of magic | he howled from afar;
Forward rode Óðinn, | the earth resounded
Till the house so high | of Hel he reached.
Although unnamed, this dog is normally assumed to be Garmr. Alternatively, Garmr is sometimes assumed to be identical to Fenrir. Garmr is sometimes seen as a hellhound, comparable to Cerberus.
The Prose Edda book Gylfaginning assigns him a role in Ragnarök:
Then shall the dog Garmr be loosed, which is bound before Gnipahellir: he shall do battle with Týr, and each become the other's slayer.
Bruce Lincoln brings together Garmr and the Greek mythological dog Cerberus, relating both names to a Proto-Indo-European root *ger- "to growl" (perhaps with the suffixes -*m/*b and -*r). However, as Ogden (2013) notes, this analysis actually requires Cerberus and Garmr to be derived from two different Indo-European roots (*ger- and *gher- respectively), and in this opinion does not establish a relationship between the two names.