Who lost their head in Norse mythology?

In Norse mythology, the god Mimir lost his head during the Aesir-Vanir war. After the conflict, the Aesir sent Mimir's head to the Vanir as a peace offering, but the Vanir instead killed him. Odin, seeking wisdom, preserved Mimir's head with magic so he could continue to consult it for advice. Mimir's head became a symbol of knowledge and insight in the mythological tales.