The earliest written versions of the Norse creation myth come from the Poetic Edda, a collection of poems found in a manuscript from the 1200s called the Codex Regius. (Old manuscripts always get cool names.) In one of these poems, the Völuspa, a mysterious wise woman called a völva tells her version of the creation of the world and predicts its end in a crazy apocalyptic battle. In another poem, the Vafþrúðnismál, the god Odin travels to the hone of a giant named Vafþrúð, where he asks the giant questions about the creation of the world and the fate of the gods.
A 13th-century Icelandic poet with the best name ever – Snorri Sturluson – borrowed bits and pieces from these poems to write the Gylfaginning (Tricking of Gylfi). The Gylfaginning is a story about a king who tries to travel to the land of the gods, but instead gets stuck in a wisdom contest in some in-between land, asking questions about the creation of the world, the gods, and the world's end in order to prove his wisdom. These three sources tell us most of what we know about the Norse creation myth.
Like creation myths in many other cultures, the Norse one imagines gods separating and organizing the cosmos into its parts. Odin and his brothers divide the cosmos into the lands of the gods, elves, dwarves, and humans. They also make the ocean, earth, and heavens. But the Norse myth has a twist. The earth is made from the body parts of a giant that the gods have brutally murdered, and the oceans, seas, and lakes form from his blood.
Why such a gory creation story? Well, the Vikings were a pretty violent group of people. Their livelihood was at least partially dependent upon the spoils of war, so a myth in which creation and order spring from death and violence seems to fit.
The landscape created from the giant's body also makes sense. In this story, the landscape is full of rocky crags and vast oceans, which is pretty much the scenery a Norseman would have seen every day. Speaking of the ocean, the Norse were big sailors. (You've probably seen lots of picture of Viking ships.) This myth's focus on the movement of the sun, moon, and stars reflects the importance of these heavenly bodies to an ocean-going people who depended upon them for navigation.
The giant Ymir, whose body-parts make up Middle-Earth, dies before all the action and of Norse mythology really gets going. But in pop culture, he's had a long and busy life. Ymir's first appearance in American pop culture was in the Marvel Comics adventure Journey into Mystery in 1963. In the comic book, Ymir is a frost-giant and one of the very first conscious beings in existence. He's also the archenemy of Odin. Marvel Comics' Ymir has not been ripped to bits to create the cosmos – at least not yet. (Check out his profile on Marvel here.) Look for Ymir's next appearance in the video game Thor: God of Thunder – he's one of the villains.