In case I didn’t have you convinced that there is an underpinning of myth in the Settlement novels, from the Wikipedia entry Berserker:
Berserkers (or berserks) were Norse warriors who are primarily reported in the Old Norse literature to have fought in a nearly uncontrollable, trance-like fury, a characteristic which later gave rise to the English word berserk. Berserkers are attested to in numerous Old Norse sources. Most historians believe that berserkers worked themselves into a rage before battle, while the idea that they consumed drugged foods has also been suggested.
The name berserker derives from the Old Norse berserkr (plural berserkir). This expression most likely arose from their reputed habit of wearing a kind of shirt or coat (serkr) made from the pelt of a bear (ber-) during battle. The bear was one of the animals representing Odin, and by wearing such a pelt the warriors sought to gain the strength of a bear and the favor of Odin.
To “go berserk” was to “hamask”, which translates as “change form,” in this case, as with the sense “enter a state of wild fury” and one who could transform as a berserker was typically thought of as “hamrammr” or “shapestrong“.