The Asgardian known as Mimir is the child of child of Buri and brother of Bor, the father of Odin and the Asgardians. Mimir was a long time enemy of his nephew Odin. It was actually Odin who transformed into a fiery being. Mimir now exists mostly as a disembodied head that dwells in the Well of Wisdom in Asgard.
Odin sacrificed his right eye to Mimir for the wisdom to prevent Ragnarök.[1] Mimir is a virtually omniscient being with precognitive abilities. Thor often travels to Hildstalf, to seek out the wisdom of the Well of Mimir. Thor sacrificed both his eyes for insight on how to permanently stop Ragnarok.[2] Mimir is shown to have been killed in the destruction of Asgard by the Thunder god himself.