In Norse mythology, Ymir, also named Aurgelmir (Old Norse gravel-yeller) among the giants themselves, was the founder of the race of frost giants and an important figure in Norse cosmology.

Snorri Sturluson combined several sources, along with some of his own conclusions, to explain Ymir's role in the Norse creation myth. The main sources available are the great Eddic poem Völuspá, the question and answer poem Grímnismál, and the question and answer poem Vafþrúðnismál.

According to these poems, Ginnungagap existed before Heaven and Earth. The Northern region of Ginnungagap became full of ice, and this harsh land was known as Niflheim.

Opposite of Niflheim was the southern region known as Muspelheim, which contained bright sparks and glowing embers. Ymir was conceived in Ginnungagap when the ice of Niflheim met with Muspelheim's heat and melted, releasing "eliwaves" and drops of eitr. The eitr drops stuck together and formed a giant of rime frost (a hrimthurs) between the two worlds and the sparks from Muspelheim gave him life. While Ymir slept, he fell into a sweat and conceived the race of giants. Under his left arm grew a man and a woman, and his legs begot his six-headed son Þrúðgelmir.

Ymir fed from the primeval cow Auðhumla's four rivers of milk, who in turn fed from licking the salty ice blocks. Her licking the rime ice eventually revealed the body of a man named Búri. Búri fathered Borr, and Borr and his wife Bestla had three sons given the names Odin, Vili and Vé.

The sons of Borr killed Ymir, and when Ymir fell the blood from his wounds poured forth. Ymir's blood drowned almost the entire tribe of frost giants or jotuns. Only two jotuns survived the flood of Ymir's blood, one was Ymir's grandson Bergelmir (son of Þrúðgelmir), and the other his wife. Bergelmir and his wife brought forth new families of jotuns.

Odin and his brothers used Ymir's body to create Midgard, the earth at the center of Ginnungagap. His flesh became the earth. The blood of Ymir formed seas and lakes. From his bones mountains were erected. His teeth and bone fragments became stones. From his hair grew trees and maggots from his flesh became the race of dwarves. The gods set Ymir's skull above Ginnungagap and made the sky, supported by four dwarves. These dwarves were given the names East, West, North and South. Odin then created winds by placing one of Bergelmir's sons, in the form of an eagle, at the ends of the earth . He cast Ymir's brains into the wind to become the clouds.

Next, the sons of Borr took sparks from Muspelheim and dispersed them throughout Ginnungagap, thus creating stars and light for Heaven and Earth. From pieces of driftwood trees the sons of Borr made men. They made a man named Ask-ash tree- and a woman named Embla-elm tree. On the brow of Ymir the sons of Bor built a stronghold to protect the race of men from the giants.