The Vikings were traders and warriors who raided and wrought hell in a paroxysm of expansion throughout Europe and the north Atlantic countries for almost 300 years from. From the 8th century to the 11th century their reputation as warriors who fought with mad unthinking fury spread as they conquered. Vikings had complex social systems, were also known to be craftsmen and eventually they settled into the territories where they expanded. The Berzerkers carry the trance-like fury myth.
The Viking King Harald Fairhair said this of them:
I’ll ask of the berserks, you tasters of blood,
Those intrepid heroes, how are they treated,
Those who wade out into battle?
Wolf-skinned they are called. In battle
They bear bloody shields.
Red with blood are their spears when they come to fight.
They form a closed group.
The prince in his wisdom puts trust in such men
Who hack through enemy shields
Berserkers were the front line raiding forces of the Viking Invaders. They were the elite, the fiercest warriors. Their name probably derives from Bear-Sark, or Bear Clothed. So they probably wore animal skins in battle, a sort of sympathetic magic.
This fury, which was called berserkergang, occurred not only in the heat of battle, but also during laborious work. Men who were thus seized performed things which otherwise seemed impossible for human power. This condition is said to have begun with shivering, chattering of the teeth, and chill in the body, and then the face swelled and changed its color. With this was connected a great hot-headedness, which at last gave over into a great rage, under which they howled as wild animals, bit the edge of their shields, and cut down everything they met without discriminating between friend or foe. When this condition ceased, a great dulling of the mind and feebleness followed, which could last for one or several days (Howard D. Fabing, On Going Berserk., p.234)