In Norse legend, the creature that is said to gnaw at the roots of Yggdrasil is Níðhöggr, a dragon often associated with decay and destruction. This creature represents the ever-looming threat of chaos that exists even within the sacred tree, which connects all realms of existence. The actions of Níðhöggr serve as a reminder of the balance between creation and destruction, reflecting deeply rooted themes of fate and destiny that permeate Norse mythology and the cosmic order.