Nidhogg, also known as
Nieddhoggr, is a fearsome monster (usually depicted as a dragon or serpent) of
Norse Mythology that gnawed on the deepest root of
Yggdrasil, the World Tree, and swore at the eagle that lived in its branches. He often used a squirrel named
Ratatosk to carry insults up and down the tree's trunk to his feathery foe. He is one of several monsters (including
Graback,
Grafvolluth,
Goin and
Moin) that were engaged in destroying the World Tree, although occasionally he stopped eating it to instead
devour human corpses. In fact, his name can be literally translated to mean "
tearer of corpses."
At Ragnarok, the mythological battle at the end of the world, Nidhogg is said to have fought at the side of Loki, the trickster God. He ultimately survives the battle to feed on the bodies of those slain.
Nidhogg is also a character in the games Age of Mythology and Final Fantasy X-2.
sources:
http://www.pantheon.org/articles/n/nidhogg.html
http://en.wikipedia.org/wiki/Nidhogg
http://www.jgmf.org/issues/JGMFIssue1.pdf
http://www.allwords.org/ra/ragnarok.html
toalight, for helpfully pointing out Nidhogg was sometimes written "Nieddhoggr."