“Berserk” is defined by the Merriam-Webster dictionary as “one whose actions are recklessly defiant.” Then there is an alternate definition given as “an ancient Scandinavian warrior frenzied in battle and held to be invulnerable.”

Nowadays, when someone snaps and loses it, he is said to have “gone berserk.”

Dr. Armando Simon published a paper in 1987 arguing that berserker rage, or Blind Rage Syndrome, should probably be included in the Diagnostic and Statistical Manual of Mental Disorders (the famous DSM). The syndrome, characterized by an over-aggressive reaction to threats be it physical, verbal, or even visual insult results in the “berserker” focusing his rage and all his strength on a target.

Dr. Simon claims his studies parallel the behavior of Viking berserkers and that the condition has been diagnosed with disorders relating to violence such as Intermittent Explosive Disorder.

It still doesn’t explain how berserkers went into a blind rage for an entire day though.

Berserkers were said to have tricks and powers they could use in combat. In Norse mythology, berserkers could simply give a menacing glance to blunt an opponent’s sword and spear.

If you’ve read Beowulf, you’ll remember all these attributes from the monster Grendel.

Take it from the Lambda Alpha Journal, a publication of Wichita State University’s Department of Anthropology:

“Grendel coincides closely with the characteristics of the berserk: Grendel seems to possess a spirit form; he undergoes transformation during his attacks on Heorot; Grendel’s appearance is horrifying; Grendel seems to have shapeshifting abilities; Grendel possesses the berserker’s famed weapons immunity; during his attacks, Grendel shows the signs of the berserker rage, including swelling and rage; after battle, Grendel falls into an extreme exhaustion or war-weariness; and finally, Grendel is set apart from the society of the Danes by his violence against that society.”

Berserkers and their other-worldly abilities have been documented outside Scandinavia, but there were other curiously fearsome warriors in other cultures.

In Malay culture, there are those who are unassuming and even peaceful, but once a weapon is at hand, they suddenly go into a frenzied craze attacking anyone within their vicinity. This is known as “running amok”.

Irish mythological hero Cuchulainn exhibited a warrior-like frenzy known as war spasms. It is found in the Irish epic Táin Bó Cúailnge:

“The Warp-Spasm overtook him: it seemed each hair was hammered into his head, so sharply they shot upright. You would swear a fire-speck tipped each hair. He squeezed one eye narrower than the eye of a needle; he opened the other wider than the mouth of a goblet. He bared his jaws to the ear; he peeled back his lips to the eye-teeth till his gullet showed. The hero-halo rose up from the crown of his head.”

The Vikings were a thriving culture of their own, and contrary to popular belief, they weren’t always the type to invade and pillage, nor did they delight in rape and murder like bloodthirsty beasts.

That image could be the result of the berserkers, who in Norse sagas, were described as “a predatory group of brawlers and killers who disrupted the peace of the Viking community repeatedly.”

Indeed, the brutish Viking image is very much like berserker behavior. In Gesta Danorum, turn of the 13th century Danish historian Saxo Grammaticus wrote:

“The young warriors would harry and pillage the neighborhood, and frequently spilt great quantities of blood. They considered it manly and proper to devastate homes, cut down cattle, rifle everything and take away vast hauls of booty, burn to the ground houses they had sacked, and butcher men and women indiscriminately.”

Berserkers were first mentioned in a Norse poem in relation to the first king of Norway, Harald Fairhair. He lived from 860 until 940.

The poem mentions warriors wearing animal skins fighting in Harald’s army.

It was in 1015 when Norway officially outlawed berserkers, and even ancient Iceland’s legal codes mentioned berserkers by branding them as outlaws.

Berserkers disappeared from any organized fighting force by the 12th century.

Berserkers were used as shock troops by Scandinavian kings like Harald and Halfdan. They would advance and clear the way so the army could move and follow while intimidating their enemies.

Berserkers and the cult of Odin were closely associated. The warriors in combat believed they were in Odin’s favor, which probably made them feel more invincible.

These berserkers were also appointed as royal bodyguards.

To “go berserk” was to hamask, or “change form.” Those who entered berserkergang were considered hamrammr, or “shapestrong.”

They say berserkers underwent a drastic physical transformation, but of course, it’s more of a figure of speech.

But in the Icelandic tale Egil’s Saga, it’s written: “the hardest of men, with a touch of uncanny about a number of them…they were built and shaped more like trolls than human beings.”

Icelandic poet and historian Snorri Sturluson, in his Ynglinga saga, describes them thus: “His men rushed forward without armour, were as mad as dogs or wolves, bit their shields, and were strong as bears or wild oxen, and killed people at a blow, but neither fire nor iron told upon them. This was called berserkergang.”

Berserkers literally put their minds into it, assuming the mental identity of the predators they wanted to channel.

This was usually a bear or a wolf, and these berserkers would eat, drink, and live in the woods to prepare themselves to be the animal they had in mind to emulate. That included drinking the blood of a bear or a wolf as well.

In the Icelandic Viking saga “Egils Sag,” Skallagrímsonar writes how one literally turned into a bear:

“Men saw that a great bear went before King Hrolf’s men, keeping always near the king. He slew more men with his forepaws than any five of the king’s champions. Blades and weapons glanced off him, and he brought down both men and horses in King Hjorvard’s forces, and everything which came in his path he crushed to death with his teeth, so that panic and terror swept through King Hjorvard’s army…”

One Icelandic poet from the 13th century wrote of a berserker who let the craze overtake him completely:

“…a demoniacal frenzy suddenly took him; he furiously bit and devoured the edges of his shield; he kept gulping down fiery coals; he snatched live embers in his mouth and let them pass down into his entrails; he rushed through the perils of crackling fires; and at last, when he had raved through every sort of madness, he turned his sword with raging hand against the hearts of six of his champions. It is doubtful whether this madness came from thirst for battle or natural ferocity.”

They feared no enemy, no weapons, and certainly not fire. This warrior did everything to psych out the enemies and once done, he went ahead and killed them anyway.

There’s no hard evidence or proof, but it’s been hypothesized that they would ingest mushrooms and get boozed up before suiting up for a fight.

Howard Fabing, in the American Journal of Psychiatry, wrote that berserkers probably took Amanita muscaria, a psychedelic mushroom containing bufotenine. Bufotenine causes hallucinations and psychophysiological effects that are consistent with how Norse sagas describe the berserkers.

Drinking a whole lot of alcohol would have been a possible cause of this behavior too.

Then again, it could have been due to self-induced hysteria, epilepsy, mental illness, and even genetics.

It’s anyone’s guess what these feared warriors did to enter such a state.

Berserkers took part in rituals resulting in what history describes as a trancelike collective state called berserkergang:

“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 colour. 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.”

Once they entered this frenzied state, berserkers would scream and howl constantly, forgetting reason and seemingly losing perception of who and where they were.

It was in this state that berserkers would fight and rip their enemies to shreds.

Berserkers would spend lots of time in extreme isolation. They would fast and expose themselves to the harsh elements, and would even engage in group weapon dances before a fight. Like shamanic secret societies, they acquired their power through ritualistic practice.

Once in isolation, these warriors would adopt the mannerisms and habits of the animal they chose to assume.

To be accepted in the group, would-be warriors were initiated by spending a period of time in the wilderness to learn the ways of the animal they were to assume. That meant hunting, gathering, and even raiding a village.

They lived like wolves, loyal to the group while proving their strength.

The candidate would then cease to be human and be more wolf or bear.

According to legend, berserkers would march into war naked, underneath the animal pelts they wore.

That means these elite Viking warriors would march on without using traditional armor.

The animal pelts they wore came from bears or wolves. Not surprising as the word “berserker” comes from the Old Norse “serkr,” meaning “coat” or “shirt,” and “ber,” the Norse word for “bear.”