Mimir is the Norse god of wisdom, and while many of the deities are known for their great degree of wise intellect, Mimir was the greatest of them all in this capacity, the Norse counterpart of Athena from the Greek pantheon and Thoth from the Egyptian pantheon. His council was greatly favored by even All-Father Odin, along with the rest of the Aesir tribe of deities. Tragedy would soon strike the wise deity soon after the Aesir picked a fight with another tribe of deities, the Vanir, who dwelt in the nearby dimensional realm of Vanaheim. The fight ended in a stalemate, and to facilitate the truce intended to lead into the merging of the two tribes, both sides agreed to an exchange of hostages. The Vanir gave the great deities Freya and Frey to the Aesir, and in return the latter gave Mimir and the warrior deity Hoenir to the Vanir. Though the Vanir were impressed by Mimir, they disliked the fact that Hoenir rarely had anything to say at all, so feeling they were partially double-crossed by the Aesir, they took out their frustration on Mimir by killing him and sending his remains back to Odin. Determined to preserve the invaluable council that Mimir provided, the All-Father used a combination of his vast power with some magickal herbs to preserve Mimir's severed head, so the deceased god could once again speak to him and have full access to his vast repository of memories and knowledge. The head of Mimir was then kept in a special chamber of Odin's palace where the king of the gods alone retained access to his great wisdom. Somehow the Well of Mimir, said to be located in some unknown section of Midgard (the Earth realm), was infused with the sum total of Mimir's great knowledge in a manner that was never fully explained in the surviving myths; Odin sacrificed one of his eyes to this sentient well in order to receive all the knowledge in the universe.
While the current status of Mimir in the cosmos is unknown, it is entirely possible for mortal followers of the Nordic path to call upon his indispensable wisdom when in need (where they will receive it largely whilst in the dream state or while in various altered states of consciousness entered into via meditation). It is not known if this wise advice is acquired from the metaphysical "remains" of Mimir or from the Well of Mimir, but ultimately it doesn't matter which since the wisdom of the universe--which Mimir personifies--is there to aid any follower of the Norse path who may wish to access it.