From Norse mythology, Yggdrasil is known as the world tree. It is the giant ash tree that links and shelters all the worlds. Beneath the three roots the realms of Asgard, Jotunheim, and Niflheim are located. Three wells lie at its base: the Well of Wisdom, guarded by Mimir; the Well of Fate, guarded by the Norns; and the Hvergelmir, the source of many rivers.
Four deer run across the branches of the tree and eat the buds; they represent the four winds. There are other inhabitants of the tree, such as the squirrel Ratatosk, a notorious gossip, and Vidofnir, the golden cock that perches on the topmost bough. The roots are gnawed upon by Nidhogg and other serpents. On the day of Ragnarok, the fire giant Surt will set the tree on fire.