The Vikings were a well traveled culture who managed to cover much of the world in their dragon ships, ranging from Canada around all the way to Turkey and parts of Russia. Though renowned as warriors, the Vikings were also great traders, poets and craftsman. The problem was that most of the history was written by people who experienced Viking raids or battles, which meant they would only have been exposed pretty much exclusively to the fury, strength and savagery of warriors who would let nothing stand between them and their goals.
Focusing on the warrior aspect of the Norsemen, there were stories that many of them were madmen in battle. Details vary but include foaming at the mouth, howling with bloodlust and even biting the rims of their shields. Tales of superhuman strength, such as Viking warriors tearing off opponent’s heads with their bare hands or shrugging off blows that should have killed them are also fairly commonplace. While these are likely the stuff of panicked battles and epic myth, there are cultural precedents in Scandinavia for warriors known as berserkers.
The berserkers were men to whom a variety of powers were attributed. Superhuman strength, invulnerability to iron and fire, as well as the ability to manifest a powerful spirit totem or to change shape into a bear or a wolf were powers associated with these warriors, some of whom were considered werewolves. Coming from the word Bjorn, for bear, berserkers often went into battle with no armor other than animal skins, such as totem animals like wolves and bears (which, given the size of some Vikings, might make you think it was a bear). The berserker were often seen dancing and shouting before battle, engaging in rituals not unlike high school football teams to drive themselves into a state of frenzy. Of course, unlike most (but not all) sports teams the berserker likely ingested a variety of substances, including a strong alcohol called mead that was made from fermented honey, to put themselves in the proper mindset. Other explanations for these recorded feats of strength and endurance include self-hypnosis, mental illness or even religious hallucination to induce the state of mind where the berserker could fight on a level that was beyond the ken of mortal men.
Most berserkers though exist only in legend and myth. For instance in the Saga of the Volsungs, Sigmundr and his son put on the skins of wolves and they then become wolves themselves. Some warriors who wore wolf skins were referred to as ulfhednar instead of berserkers, which were supposed to be warriors chosen by Odin who was a god of war and battle. The powers the ulfhednar possessed were almost identical to the berserker, except that the totem animal was a wolf rather than a bear.
Myth and epic tales aside however, the berserker were most likely gifted warriors who were members of the cult of Odin. These warriors were highly skilled, strong and driven by a religious fervor and used as shock troops for their skills. Their screaming, wearing of animal skins and the strength they displayed (driven by adrenaline that any warrior entering battle would be running on like a NOS unit in a pinto) would all have been terrifying to the enemy and carefully calculated to crush the will to fight these monsters just as their tactics and weapons were meant to destroy the soldiers who stood in their way.
“Berserkergang,” by The Viking Answer Lady at Viking Answer Lady
“Berserker,” by Anonymous at Yahoo Education