In Norse mythology, Ymir, Aurgelmir, Brimir, or Bláinn is the ancestor of all jötnar. Ymir is attested in the Poetic Edda, compiled in the 13th century from earlier traditional material, in the Prose Edda, written by Snorri Sturluson in the 13th century, and in the poetry of skalds. Taken together, several stanzas from four poems collected in the Poetic Edda refer to Ymir as a primeval being who was born from venom that dripped from the icy rivers Élivágar and lived in the grassless void of Ginnungagap. Ymir birthed a male and female from the pits of his arms, and his legs together begat a six-headed being. The gods Odin, Vili and Vé fashioned the Earth (elsewhere personified as a goddess; Jörð) from his flesh, from his blood the ocean, from his bones the hills, 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. In addition, one stanza relates that the dwarfs were given life by the gods from Ymir's flesh and blood (or the Earth and sea).