Some characters in Norse mythology don’t fit into any of the established categories of beings that populate these tales (Aesir and Vanir deities, giants, elves, etc.), or their affiliations with such groups are ambiguous or unknown due to the fragmentary nature of the sources we have concerning the mythology and religion of the pre-Christian Norse and other Germanic peoples. Such beings include the Norns, who create the fate of all beings; Mimir, an exceedingly wise being who is either an Aesir god or a giant; and Sleipnir and Hugin and Munin, three of the numerous familiar spirits of the god Odin.

The Ultimate Online Guide to Norse Mythology and Religion