Mimir

Mimir was a primal god of Norse mythology whose head was severed during the war between the Aesir and the Vanir deities. He was renowned for his knowledge and wisdom and the god Odin journeyed to the land of the giants, Jotunheim, to acquire Mimir's omniscient wisdom and knowledge for himself. The knowledge was attained by drinking from Mimir's magical well, but as a price for drinking of it Odin was forced to pluck out one of his eyes. Odin returned to Asgard with Mimir's heads for oracular consultation according to some accounts. Mimir was also Honir's chief advisor after he became a ruler of the Vanir.

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Mimir was also the name of the dwarf that fixed Sigurd's father's sword in Norse mythology.

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A mimir is also a magical construct that is created to provide information to players in the Dungeons & Dragons role playing game Planescape setting. They are usually a silvery, metallic, disembodied skull (most likely derived from the definition above).