Níðhöggr

Níðhöggr or Nidhogg (Old Norse: Níðhǫggr, meaning "Curse-striker" or "He Who Strikes with Malice") is a powerful dragon that is found in Norse Mythology.

Myths & Legends
Níðhöggr lives in the roots of the great ash tree Yggdrasill which holds the 9 realms of Norse cosmology together. Níðhöggr also chews on the roots of the tree for all eternity with hopes to damage it and topple it. Níðhöggr was one of many lindworms (a serpentine Norse dragon) slithering around the world tree and chewing on it, but he is the most well known one. Níðhöggr has never left the roots of Yggdrasil, and it is presumed that he was born and raised there.

He has a rivalry with an eagle that lives at the top of the World Tree and the two exchange harsh words and messages through Ratatöskr, the giant mischievous squirrel, who acts as a messenger. Níðhöggr is aligned with the Norse Giants known as Jǫtunn.

Níðhöggr is also said to preside over a part of the underworld called Náströnd ("The Shore of Corpses") where perjurers, murderers, and adulterers are punished. However, this may be the result (one of many) of Christian influences.

Appearance
Níðhöggr is an immense Norse dragon known as a linnormr, which are serpentine (similar to oriental dragons) and are known for only having two front claws and no other limbs. He is gigantic enough to cause serious damage to a tree the size of the universe, which indicate that he has very tough and sharp fangs. He has spines going all along his back, and two horns.

Ragnarök
When the Norse apocalypse known as Ragnarök arrives, Níðhöggr will fly out from the roots of Yggdrasill in order to aid the Jotunn in their battle against the gods. This is specifically noted in the Old Norse poem the Völuspá or “Insight of the Seeress."