One of the great mythological dogs of Scandinavian tradition, Garm (Garmr) guards the mouth of Hel and is described as having four eyes and being permanently spattered with blood. He is said to be particularly savage towards those who did not show kindness to others in life. He will howl loudly at the start of Ragnarok the end of time. At the finish of the day, when only he and the one-handed god Tyr are left standing they will slay each other.
John and Caitlin Matthews, The Element Encyclopaedia of Magical Creatures, 2013, Garm, p 190