Odin is one of the prominent gods of Norse Paganism. You will meet Odin in the game during the second act. He travels through Britannia and he will visit your camp at some point, disguised as an old traveler by the name of Grimnir. After that, he will visit your dreams three times.
Grimnir will take you to Helheimr during the first dream, where you will see all prominent and less known enemies you have slain so far. The less known enemies will walk as transparent figures pass you, while enemies such as Ottarr Erlingsson and Ingimar Broad-sole will be standing near the starting point.
During the second dream, you will be taken to high mountain. On top of the mountain, there stands a throne which is guarded by two wolves.
During the third dream, he will take you an event of Ragnarok, which also starts the quest Charge of the Einherjar.
During the first and second dream, you can hear some soundtracks which are only used during those dreams.