Berserkers, so prominent in Hrolf's Saga, are the remnants in Christian times of older stories. In pre-Christian Scandinavia, berserkers seem to have been members of cults connected with Odin in his capacity as god of warriors. Snorri Sturluson in Ynglinga Saga, recalling numerous elements of ancient lore, describes Odin's warriors in this way:

His men went to battle without armor and acted like mad dogs or wolves. They bit into their shields and were as strong as bears or bulls. They killed men, but neither fire nor iron harmed them. This madness is called berserker-fury.
The berserkers of the saga, who often appear as the core of the king's warband, are at times reminiscent of the retinue of warriors surrounding Odin and may ultimately derive from ancient bear cults. Debate has centered on the meaning of the word itself. Berserker could mean "bare shirt," that is, naked; berserkers, as a mark of ferocity and invincibility, are said to have fought without needing armor. The word, however, may also mean "bear-shirt," reflective of the shape and nature of the bear assumed by these warriors. More literally, it may refer to protective bearskins that such warriors may have worn into battle. When the "berserker rage" was upon him, a berserker was thought of as a sort of "were-bear" (or werewolf), part man, part beast, who was neither fully human nor fully animal. Although not specifically so called, Bodvar Bjarki is a berserker of sorts. He appears at Hrolf's final battle in the form of a huge bear, invulnerable to weapons. In both his invulnerability and his ability to change shape, Bodvar also displays preternatural abilities resembling those of Odinic champions.