Ratatoskr

Ratatoskr (Old Norse: Ratatoskr) is a squirrel that lives in and runs along Yggdrasil, the world tree. His sole function is to carry provocative and insulting messages between the eagle perched at the top of Yggdrasil and the dragon Níðhöggr gnawing at its roots. Ratatoskr is not dangerous in himself, but his ceaseless gossip and mischief maintain the enmity between crown and root — and thus slowly weaken the world tree.