Ymir is a primeval being born of primordial elemental poison and the ancestor of all jötnar or Frost Giants. Ymir was born when fire from Muspelheim and ice from Niflheim met in the abyss of Ginnungagap. Ymir was suckled by the cow Auðhumla for his nourishment, and several other giants spontaneously sprang from his sweat.
Despite being the progenitor of the Jotunns and gods, Ymir was by no means considered a god, and is stated that "he was evil and all his descendants". Ymir is the ancestor of all jötnar (specifically hrimthursar), and that it is said that when Ymir slept, he sweated, and from his left arm and right arm grew a male and a female, and his left leg produced a son with his right leg, and from them came generations.
The cow licked salty rime-stones to produce the milk that is necessary to sustain Ymir. The first day Auðumbla licked the rime stones it uncovered that evening the hair of a man. The second day it uncovered his head. The third day a man was uncovered from the ice. This man was named Búri, and was large, powerful, and beautiful to behold. Búri later produced a son by the name of Borr who married a giantess named Bestla. The two had three sons; Odin, Vili and Vé.
Odin, Vili, and Vé later decided to attack and successfully kill Ymir, and his body produced so much blood from his wounds that within it drowned all the jötnar but two, Bergelmir, who, on a lúðr with his (unnamed) wife, survived and repopulated the jötnar. Earth was fashioned from his flesh, from his blood the ocean, from his bones the hills, scree and stones his teeth, molars, and bones. From his hair the trees, from his brains the clouds, from his skull the heavens, and from his eyebrows the middle realm in which mankind lives, Midgard.