In Norse mythology, the wisest of the gods of the tribe Aesir .
He was also believed to be a water spirit. Mimir was sent by the Aesir as a hostage to the rival gods (the Vanir ), but he was decapitated and his head was returned to the Aesir. Odin preserved the head in herbs and gained knowledge from it. Other tales claim that Mimir lived by a well beneath the roots of Yggdrasill , the world tree, and that he was a smith who taught the hero Siegfried his craft.