Every morning, in the account Snorri Sturluson sets down in the Prose Edda, Odin sends out two ravens named Huginn and Muninn to fly across the whole world. They return by the time of his morning meal and perch on his shoulders to tell him everything they have seen and heard, which is why, Snorri writes, Odin is called Hrafnagud, the raven god, and why he is said to know so much of what happens far beyond his own hall. The names themselves carry the point directly: Huginn is Old Norse for thought, Muninn for memory, so the pair are not simply Odin's pets or messengers in a generic sense but a working extension of his own mind, sent out precisely because thought and memory are exactly what a figure needs to know a world he cannot personally watch at every moment.
The single line of dialogue Snorri gives Odin about them is unusually candid for a god otherwise defined by cunning and concealment: Odin says he worries for Huginn, that thought might fail to return, but he worries still more for Muninn, memory, suggesting that even for the Norse tradition's most knowledge-hungry god, losing the capacity to remember was reckoned worse than losing the capacity to perceive in the moment. The Poetic Edda poem Grimnismal independently names the same two ravens in a scene where Odin, disguised and bound between two fires, recites a long catalogue of cosmic knowledge; that the ravens appear again there, in a wholly different poetic context from Snorri's prose account, is part of why scholars treat the pairing as an old and stable piece of the tradition rather than as one author's invention.