In Norse mythology, Odin sacrificed an eye to gain wisdom from Mímisbrunnr.
Mímisbrunnr, usually called Mímir’s well in English, was a well beneath one of the roots of the world tree Yggdrasil. Its waters were associated with knowledge and wisdom. According to the Prose Edda, Odin gave one of his eyes to Mímir in exchange for permission to drink from the well.
The story helps explain why Odin is portrayed as a god who relentlessly seeks knowledge, even at great personal cost. His missing eye is one of his most recognizable features in Norse mythology. The sacrifice is sometimes confused with Odin’s later ordeal of hanging on Yggdrasil, during which he learned the runes; these are separate episodes.
Odin was also associated with kingship, war, poetry, magic and the dead. Mímir appears elsewhere in the myths as a wise figure whose severed head Odin preserves and consults, linking him closely with hidden knowledge.