The wild men of the North.
You never forget a close encounter with a wild animal bent on hunting you down for their next meal. It is one of the terrifying experiences you could ever have. Now imagine being approached by a stealthy creature with the face of a man and the head of a bear or wolf brandishing sword and shield. The creature wild-eyed almost foaming at the mouth. Wouldn't that terrify you? This is a good description of the Berserker a Norse warrior who fought in a trance-like uncontrollable fury, a characteristic which caused the English to create a new word to describe them, the 'Berserk'.
Berserkers appear in many poems and sagas. They describe Berserkers as ravenous men who kill, plunder, and loot indiscriminately. In later dates, Christian interpreters described Berserkers as "heathen devils".
The 9th-century skaldic poem composed by Thórbiörn Hornklofi is one of the earliest surviving references for "Berserker" found in Haraldskvæði. The poem was written as an honor for King Harald Fairhair, as ulfheðnar "men clad in wolf skins". Below is a translation from the Haraldskvæði saga:
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.
Snorri Sturluson 1179–1241 an Icelandic poet and accomplished historian wrote the following description in his Ynglinga saga about the Berserker: