Niederhogg (Old Norwegian: N í ð H ö ggr, N í ð H ǫ Ggr, English spelled: Nidhogg, meaning "malicious attacker", is the daughter of the Yggdrasil in Nordic mythology, a black dragon occupying the bottom of the Yggdrasil. It, along with countless venomous snakes, kept gnawing at its roots until it was ultimately destroyed.
Nedehog and the eagle Ve, who lives at the top of the World Tree ð RF ö lnir) formed a grudge against each other, and a squirrel named Ratat ö skr often conveyed jealous words between them. Niederhaug was prophesied to depart from the dark mountains of the northern underworld (Ni) after the twilight of the gods ð Afj ö ll) flies out, flapping its wings and carrying the corpse.
Nederhogg will also appear in N á str ö nd, an area of the underworld where perpetrators of murder, adultery, and breaking vows will have to wade through drug waters, while Nederhogg is responsible for chewing them.
The name of Niederhaug and the ancient Norwegian word 'N' īþ” Regarding, N īþ It specifically refers to a villain who has lost honor and status.

There are various ways to write the word 'Nidhogg': Nidhogg, Nidhoggr, Nithhogg, Nidh ö gg, Nidh ö ggr, Nithh ö ggr, N í dh ö ggr, Nithhoggr, Nidhhogg, N í ð H ö gg, Ni ð Hoggr, N í ð Hoggr, N í dh ö gg, Hidhaegg, or Nidhhoggr. The English writing method is: Nidhoggur. In Danish, it may be expressed as Nidhug or Nidhog. The modern Icelandic form is N í ð H ö ggur, Norway is Nidhogg, Sweden is Nidh ö gg, and Denmark is Nidhug and Nidh ø g.
Niederhaug is only mentioned in Snorri Sturlusson's "Ida in Poetry" and "Ida in Prose", and is not mentioned in any other ancient literature.
In the chapter "Deception of Gurufi" in Essay Ada, it is mentioned that the Tree of the World has three main roots, and one of the roots is located next to the Hvergelmir spring in Niflheim, where Nederhogg desperately wants to devour the Tree of the World, and there are also many venomous snakes helping him, usually nameless. When they bite through the roots of the tree of the world, the 'twilight of the gods' will also come.
In the section 'Sk á ldskaparm á l', Niederhaug is designated as a snake in a list of names. And in another list of names related to swords, it includes the name of Nederhogg.
In "The Prophecy of the Witch" in "The Poetic Ada," Niederhaug places the deceased on his wings and flies towards the sky.

In Nordic mythology, the World Tree, which connects the nine worlds, has a total of three tree roots, each of which draws water from three springs to continuously strengthen the World Tree. One of the roots of the tree extends into the Hervagamir Spring in the foggy country of Niforheim, and the venomous dragon Nedhog lurks next to the Hervagamir Spring, nibbling on it with countless snakes. When they bite off the roots of the tree, the tree of the world will wither, and the 'twilight of the gods' will come.
(Note: It must be clearly stated here that the reason for the occurrence of the "twilight of the gods" is not due to Niederhogg biting the tree root. Niederhogg biting the tree root is only a precursor to the arrival of the "twilight of the gods", not its cause. It leads to the "twilight of the gods" The real reason for this is the hatred accumulated through years of war between the gods and the giant race, so the two camps are destined to trigger a final battle to end all of this
In addition to mentioning Nederhogg's gnawing of tree roots, there is also a grudge between Nederhogg and the eagle Vedfolnir at the top of the World Tree, and Ratatosk, the squirrel, is their instigator. In addition, it also gnaws at the souls of the deceased who were thrown to Nastrond after death due to their many wrongdoings. When the "twilight of the gods" arrives, it will flutter its wings, fly full of dead bodies on the battlefield, and finally be weighed down by the weight of the dead bodies, falling back into the abyss. Nedehog is also one of the few creatures to survive after the 'twilight of the gods'.