So the "creature" is (Spoiler Alert!)

More like a man-serpent-polar bear, I'd say.

A Sasquatch/Polar Bear mix breed.

Tuunbaq, a ravenous beast whose lust for blood is never sated and whose origins are shrouded in mystery. The Tuunbaq stalks and kills the men of the expedition , but seems to have some sort of relationship with the indigenous people of the North.

Fictional monster of course but would be nice if it was based off of an actual Inuit myth. Closest I could find was Ijiraat, shapeshifters that may change into any arctic animal but may not disguise their red eyes.

https://d12qk6n9ersps4.cloudfront.net/5446316/medium-clean.jpg

Also closely resembles an extinct short-faced bear.

If I could tuunbaq time
If I could find a way
I'd take back those words that hurt you
And you'd stay

SPOILER (From the book) It's a spirit with a physical body. He hunted the natives until some powerfull shaman learned how to control it and to exile it in the arctic wasteland, far from the villages. Dealing with it is a traditional role.

When the actual shaman was killed, Tunnbaq was free, pissed of and very unhappy (he needed a shaman to take care of him).

I'm somewhat disapointed with the end of the serie, because Tunnbaq can't be killed. He will eventually come back

In the book, the captain stayed with lady silence to take care of him, and becoming the new shaman. It made sense.