In Norse mythology it is said that two races of deities ended up in Asgard, the Aesir and the Vanir. The Vanir goddess Gullveig (Gold-Thirst) went to the Aesir and flaunted her ability to predict the future and make gold.
When she refused to share her secrets with them, the Aesir killed and burned her. This proved ineffective. Twice Gullveig rose from the flames. Finally the Aesir gave up. They renamed her Heid (Gleaming One) and began to consider a peaceful life with the Vanir more seriously.
However, the murder attempt brought about constant fighting, with neither side getting the upper hand. The walls of both kingdoms were destroyed. Finally a truce was called and hostages exchanged.
The greatest Vanir deities, Njord, Frey and his sister Freya (supreme goddess of Magic), joined the Aesir.
Meanwhile, the Vanir were having their own problems, with the two Aesir hostages, Mimir and Hoenir. Mimir was very wise, but Hoenir was mostly silent. When he did speak, it was evident that he was not very bright. In disgust, the Vanir took out their frustrations on Mimir, relieving him of his head that they sent back to Odin.
The Allfather, Odin preserved it with herbs and placed it at the fountain in Midgard, so that Mimir's knowledge would not be lost.
When Mimir was slain, his seven sons fell asleep in their hall in Hel. When Heimdall blows his horn at Ragnarok, Mimir's sons will awake and fight the Gods of Asgard against their enemies.
Brightest of Blessings,