How did Odin lose his eye?

Odin, king of the Norse gods, gave up his eye in exchange for a drink from a well of wisdom. Although Odin already had much knowledge, he desired to understand everything.

Mimer, an ancient giant, guarded the well. Odin approached him and offered to pay any price in order to drink the well's water. The giant was reluctant to grant the request, because it would give great power to an enemy of the giants. Thinking that Odin would refuse, Mimer agreed, provided that Odin leave one eye at the bottom of the well. Odin was torn, but his longing for wisdom won. After drinking a horn full of water, Odin plucked out his eye, completing the bargain.