Odin's quest for knowledge includes Huginn and Muninn (pronounced as HOO-gin and MOO-nin, where sometimes it is anglicized into Hugin and Munin), his pair of ravens. The pair scout Midgard in search of information to bring back to Odin himself to help keep as him omnipotent as possible. Specifically, the ravens would return at dinner time allowing Odin to remain up to date on a day to day basis. Huginn and Muninn were documented in the Poetic Edda in the 13th century (an unnamed collection of Norse poems).
Odin is sometimes referred to as the raven god (amongst countless other names) given the ravens would spend any time not gathering knowledge on the shoulders of Odin himself. He also has been documented in the Poetic Edda as showing concern over his ravens not returning whilst disguised as Grimnir. Odin specifically was more worried about Muninn.
Here is an exert from the Edda translated by Benjamin Thorpe:
Hugin and Munin fly each day
over the spacious earth.
I fear for Hugin, that he come not back,
yet more anxious am I for Munin
In the Heimskringla book Ynglinga saga, it is said that Odin bestowed the ravens with the gift of speech as well. There is little information on how Huginn and Muninn utilized this ability, unfortunately.
Rudolf Simek is critical of the idea of Huginn and Muninn as literal ravens and thinks that they may be more-so referring to the god's powers of intellect, rather than separate entities.
Ravens, in general, hold great significance in Norse culture. A sacrifice to Odin where shortly after ravens are sighted indicates that the sacrifice was accepted. Ravens specifically were linked with Odin, as Odin was a god of war and death. Ravens are still known to be carrion birds, meaning where decaying flesh is found, these birds are shortly to be found soon after. They're also exceptionally intelligent, making them the perfect choice for a god consumed by the pursuit of omnipotence. Huginn, meaning thought, and Muninn, meaning memory, are interesting symbols given the words themselves are so similar. It is said that the pair has no difference in personality and that they were simply duplicates of the same idea.
In this time, it was said that the 'self' is compromised of numerous detachable parts. Linking in with Rudolf's opinion on the ravens not being separate entities, it could be argued the ravens are detachable parts of Odin's self, to begin with. More interestingly, whenever one would separate from himself, there was always the risk he would not become whole again. This ties in with our earlier discussions of Odin worrying the pair would not return, or more specifically that his Muninn meaning memory. Odin was/is obsessed with the pursuit of knowledge, and what could be worse than losing previously earned knowledge?
Whilst the 2 ravens generally are identical, there are records of them showing specific roles separate from one another, for example, In the Third Grammatical Treatise, a comment is made stating "Two ravens flew from Hnikar’s [Óðinn’s]:shoulders; Huginn to the hanged and:Muninn to the slain [lit. corpses]."