Mythology, Ratatosk is the squirrel
that runs up and down the world tree Yggdrasil
One translation reads...
"Ratatosk the squirrel is called which runneth
about the ash Yggdrasil:
the warning words of the watchful eagle
he bears to Nidhogg beneath."
Other interpretations have him carrying news and/or insults from the great dragon Nidhogg to the eagle and hawk above.