Berserkers (or Berserks) were Norse warriors who had sworn allegiance to the sky god Odin. They worked themselves into murderous fury before a battle. The term berserker comes from Norse "berserkr", meaning literally "bear shirt", but alluding to wearing the "clothes" of a bear, i.e. to be bear-like in rage and strength, usually in battle.
The origin of berserkers is unknown, although Tacitus mentions groups of Germanic warriors with berserk-like fury. It appears that berserkers were religiously-inspired warbands or warrior societies. Norse sagas mention berserker gangs with twelve members where new applicants had to go through a ritualistic or real fight to be accepted. Some berserks also took names with björn or biorn in them in reference to a bear.
Many northern kings used berserkers as part of their army of hirthmen and sometimes equivalent to a royal bodyguard. It may be that at least some of those warriors just adopted the organization or rituals of berserk warbands or used the name as a deterrent or claim of their ferocity. It is doubtful any king would have accepted a band of homicidal maniacs as his closest men.
In 1015 King Eirik Bloodaxe of Norway outlawed berserkers. Icelandic Christian law banned berserkers as heathens and sentenced them to outlawry. By the 1100s organized berserker warbands had disappeared.
One explanation behind beserker rage, suggested by botanists, is that in Scandinavia, one of the main spices in alcoholic beverages was the plant bog myrtle (Gale palustris). The drawback is that it increases the hangover headache afterwards. Drinking alcoholic beverages spiced with bog myrtle the night before going to battle, might have resulted in unusually aggressive behavior.
Those who believe in the existence of spirit possession favor a theory that the berserk rage was brought on by possession by an animal spirit of either a bear or a wolf. According to this theory, berserkers were those who had cultivated an ability to allow the spirit of a bear or wolf to take over their body during a fight. This is seen as a somewhat peculiar application of animal totemism.
