Mimir

Mimir is the wise being who keeps the well of wisdom under a root of Yggdrasil, where Odin pledged one of his eyes for a single drink. Beheaded by the Vanir, who held him as a hostage, he goes on advising Odin as a head preserved by magic.

In Gylfaginning, Snorri Sturluson places Mimir's Well under the root of the World Tree that reaches toward the frost giants. It holds wisdom and understanding, and its keeper is full of ancient lore because he drinks from it with the horn Gjallarhorn. Odin was granted a single drink only after leaving his eye in the well as a pledge. Snorri follows Voluspa, whose seeress tells Odin she knows his eye lies in Mimir's famous well, where Mimir drinks mead every morning from the pledge of the Father of the Slain.

Ynglinga saga, in Snorri's Heimskringla, tells another story. To end their war, Aesir and Vanir exchange hostages: the Vanir send Njord and Freyr, and the Aesir send Hoenir together with Mimir, “the wisest of men”, receiving Kvasir in return. The Vanir make Hoenir a chieftain, but without Mimir at his side he can only answer “let others decide”. Feeling cheated, they behead Mimir and send the head back. Odin smears it with herbs against decay and sings charms over it until it speaks and tells him many hidden things; he carries it with him, and it brings him news from other worlds. In Sigrdrifumal the head speaks wise words about the runes, and in Voluspa, as Heimdall blows the Gjallarhorn at the start of Ragnarok, Odin consults Mimir's head; Snorri has him ride to the well for counsel.

The sources never reconcile the keeper of the well with the beheaded hostage, nor name his parents. Some scholars identify him with the unnamed son of Bolthorn, brother of Odin's mother Bestla, who teaches Odin nine mighty songs in Havamal, but no text says so. Voluspa also mentions “Mim's sons” stirring at the end of the world without saying who they are. His name is usually linked to memory.