In Norse mythology, Níðhöggr is the dragon that gnaws at the roots of Yggdrasil.
Yggdrasil is the immense world tree connecting the principal realms of Norse cosmology. Níðhöggr lives beneath the tree, near the roots associated with the underworld realm of Niflheim or Hel. The dragon feeds on corpses and continually gnaws at the tree’s roots, embodying decay and the destructive forces beneath the ordered cosmos.
The Poetic Edda and Prose Edda also describe a hostile exchange involving Níðhöggr and an unnamed eagle in the tree’s crown. A squirrel named Ratatoskr carries messages between them, spreading conflict along the trunk. This imagery makes Yggdrasil a living ecosystem rather than a motionless cosmic diagram.
Níðhöggr is often confused with Jörmungandr because both are huge serpent-like beings. Their roles are different: Jörmungandr encircles Midgard and fights Thor, while Níðhöggr remains beneath Yggdrasil and is associated with the roots, the dead, and cosmic deterioration.