In Northern European creation myths, at the dawn of time there was neither heaven nor earth. Amid dense mist lay only Ginnungagap. To the north of the chasm was Niflheim, the "Land of Mist," while to the south was Muspelheim, the "Land of Fire." Where heat and frost mingled, Ymir, ancestor of the giants, and an enormous cow named Audhumbla were born. Ymir survived on the milk Audhumbla produced, while Audhumbla licked the salt from the ice. Later, the wise giant Mimir and the giantess Bestla grew from Ymir's body. Under the cow's licking, Buri, ancestor of the gods, emerged from the ice. Buri begot Bor, and Bor and Bestla, the giantess of the frost giants, begot Odin, Vili, and Ve.
The giants and the gods were at odds, and war broke out between them. Later, Ymir was slain by the gods. The giants were defeated and fled to Jotunheim, retaining their hatred for the gods as they waited for a chance to avenge themselves. The gods used Ymir's blood to create the seas, his sweat for lakes, his body for the earth, his bones for mountains, his beard for plants, his teeth for rocks, his skull hung aloft for the vault of heaven, and his brains for clouds, recreating the world.
In this newly created world stood a "World Tree" named Yggdrasil. It was said to be an ash tree, and Odin's spear had been made from one of its branches.
In Old English, Ygg meant "terrifying," and it was also another name for Odin. Drasil referred to a horse, so together they meant "Odin's horse." It was said to commemorate how Odin had once hung himself upside down from the tree and pierced himself with his spear, thereby discovering the runes.
There were nine realms upon this tree.