Norse cosmology employs a full-time professional troublemaker, and he is a squirrel.
Grímnismál stanza 32 is his entire attested existence: Ratatoskr is the name of the squirrel who shall run on the ash Yggdrasil; he carries down from above the eagle's words and tells them below to Níðhöggr.
Snorri expands it very slightly in Gylfaginning, saying that the squirrel runs up and down the ash and carries spiteful words between the eagle and Níðhöggr — adding the malice, which the poem leaves implicit.
Nothing else. No origin, no fate, no Ragnarök role, no genealogy, no worship, and no story in which he does anything besides the running.
Why this is not a decorative detail
The tree has three parties in permanent hostile relation. At the top, an unnamed eagle of great knowledge, with a hawk called Veðrfölnir perched between its eyes. At the bottom, Níðhöggr, gnawing the root. In between, the trunk, which is the whole of the world.
Neither the eagle nor the dragon can reach the other, and neither would understand the other's abuse if it were shouted. So there is a courier. The structure of the cosmos requires a means of transmission for hostility, and Norse myth supplies a dedicated post for it.
The four harts browse the tree. The serpents chew the roots. The norns water it. And the squirrel keeps the quarrel going. Every creature named on Yggdrasil is engaged in either damage or maintenance, and Ratatoskr's contribution is neither: he supplies the reason the damage continues.
The name is a linguistic mess
Ratatoskr has no agreed etymology and the attempts are unusually varied.
- The second element is generally read as toskr, tusk or tooth — so "drill-tooth," "gnaw-tooth," or "bore-tooth."
- The first element has been read as rata, to travel or to find one's way, giving "the one who finds his way with his teeth"; or as connected to rata meaning to bore or drill, which would echo Rati, the auger Odin uses to bore into the mountain for the mead of poetry.
- A quite different proposal takes the whole name as a Norse rendering of a borrowed word for a rat or a small rodent, with the second element reanalysed to make sense in Old Norse — which would make the most famous squirrel in world mythology the product of a mishearing.
None has closed the argument. What everyone agrees on is that the name is about teeth, which for a rodent on a tree that is being chewed to pieces is thematically apt whether or not it is intentional.
Squirrels, actually
Red squirrels are native across Scandinavia and were economically significant — squirrel pelts were a real trade good in the Viking-age and medieval north, moving in bulk out of Russia and Scandinavia into western European markets, and they appear as a currency-adjacent commodity in Novgorod records. Anyone in Iceland or Norway would have known the animal's behaviour: fast vertical movement, chattering vocalisation, ceaseless activity.
The observation behind the myth is exact. A squirrel does spend the day running up and down a tree making noise, and if you were assigning a job to one, message-carrying is what you would pick.
The interpretations
Some readers take the eagle-and-serpent opposition as a widespread Indo-European or near-universal image, with parallels adduced from Indian and Mesopotamian material, and Ratatoskr as the Norse addition to it. The comparison is reasonable and the transmission unproveable.
Others read the squirrel as an image of slander itself — rógberandi, the carrier of strife, a recognised social type in a culture where an insult could start a feud and where formal slander was legally actionable. Icelandic sagas are full of the person who takes a remark from one household to another and watches what happens. Ratatoskr is that person, given a permanent office in the structure of the universe.
Why the squirrel is so popular
He is the most popular minor figure in Norse mythology by a wide margin, largely because the image is funny and immediately graspable. He appears in God of War, in comics, in children's books, on merchandise, and gave his name to a Norwegian ferry, an American snowboarding brand and a metal band or two. In a mythology usually reduced to hammers and wolves, a gossiping squirrel is refreshing.
For the tree, see Yggdrasil; for the two parties he carries words between, Níðhöggr; and for the Norse overview.
What does the eagle at the top of the tree represent?
The sources do not name it and do not say. It sits in the branches with great knowledge, has a hawk called Veðrfölnir between its eyes, and is otherwise a blank. Some readers connect it to the eagle-form Odin takes when escaping with the mead of poetry, or to the giant Hræsvelgr, "corpse-swallower," who sits at the end of the sky in eagle shape and makes the wind with his wings — but Grímnismál and Vafþrúðnismál keep them separate. Whatever it is, it is the only creature on the tree that neither eats it nor repairs it.
Does Ratatoskr have any role in Ragnarök?
None is recorded, and no source mentions him again. Given that the tree survives the fire in most readings, and that the eagle and the dragon both appear in end-of-the-world contexts, the silence is a genuine gap rather than a statement — but it does fit the shape of the material. Ratatoskr belongs to the cosmology's ongoing operation rather than to its narrative, and the poems only tell stories about things that end.