Níðhöggr in the context of Germanic dragon

Yggdrasil (from Old Norse Yggdrasill) is an immense and central sacred tree in Norse cosmology. Around it exists all else, including the Nine Worlds.

Yggdrasil is attested in the Poetic Edda compiled in the 13th century from earlier traditional sources, and in the Prose Edda compiled in the 13th century by Snorri Sturluson. In both sources, Yggdrasil is an immense ash tree that is central to the cosmos and considered very holy. The gods go to Yggdrasil daily to assemble at their traditional governing assemblies. The branches of Yggdrasil extend far into the heavens, and the tree is supported by three roots that extend far away into other locations; one to the well Urðarbrunnr in the heavens, one to the spring Hvergelmir, and another to the well Mímisbrunnr. Creatures live within Yggdrasil, including the dragon Níðhöggr, the squirrel Ratatoskr, the hawk Veðrfölnir, and the stags Dáinn, Dvalinn, Duneyrr and Duraþrór.

Hvergelmir (Old Norse "bubbling boiling spring") is an important primal wellspring in Norse mythology. Hvergelmir is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson. In the Poetic Edda, Hvergelmir is mentioned in a single stanza, which details that it is the location where liquid from the antlers of the stag Eikþyrnir flow, and that the spring, "whence all waters rise", is the source of numerous rivers. The Prose Edda repeats this information and adds that the spring is located in Niflheim, that it is one of the three major springs at the primary roots of the cosmic tree Yggdrasil (the other two are Urðarbrunnr and Mímisbrunnr), and that within the spring are a vast amount of snakes and the dragon Níðhöggr.

In Norse mythology, Ratatoskr (Old Norse, generally considered to mean "drill-tooth" or "bore-tooth") is a squirrel who runs up and down the world tree Yggdrasil to carry messages between the eagles perched atop it and the serpent Níðhöggr who dwells beneath one of the three roots of the tree. Ratatoskr is attested in the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson.