In Norse mythology, what is the name of the serpent which eats the roots of the ash tree Yggdrasil?

In Norse mythology, the name of the serpent that eats the roots of the ash tree Yggdrasil is Nidhogg. Nidhogg is a fearsome dragon-like creature that resides in the underworld and constantly gnaws at the roots of Yggdrasil, seeking to bring about its destruction and plunge the world into chaos. It is believed that Nidhogg's actions symbolize the constant threat of decay and destruction that exists in the world.