Berserkers (or berserks) were champion Norse warriors who are primarily reported in Icelandic sagas to have fought in a trance-like fury, a characteristic which later gave rise to the English word berserk.
These champions would often go into battle without mail coats. Berserkers are attested to in numerous Old Norse sources, as were the Úlfhéðnar ("wolf-coats").
The English word berserk is derived from the Old Norse words ber-serkr (plural ber-serkir) possibly meaning a "bear-shirt"—i.e., a wild warrior or champion of the viking age, although its interpretation remains controversial. The element ber- was interpreted by the thirteenth-century historian Snorri Sturluson as "bare", which he understood to mean that the warriors went into battle bare-chested, or without armor. This word is also used in ber-skjaldaðr that means "bare of shield", or without a shield. Others derive it from the preferred berr (Germ, bär = ursus, the bear), and Snorri's view has been largely abandoned.
It is proposed by some authors that the northern warrior tradition originated in hunting magic. Three main animal cults appeared: the bear, the wolf, and the wild boar.
The bas relief carvings on Trajan's column in Rome depict scenes of Trajan's conquest of Dacia in 101–106 AD. The scenes show his Roman soldiers plus auxiliaries and allies from Rome's border regions, including tribal warriors from both sides of the Rhine. There are warriors depicted as bare-foot, bare-chested, bearing weapons and helmets that are associated with the Germani. Scene 36 on the column shows some of these warriors standing together, with some wearing bearhoods and some wearing wolfhoods. Nowhere else in history are Germanic bear-warriors and wolf-warriors fighting together recorded until 872 AD, with Thórbiörn Hornklofi's description of the battle of Hafrsfjord when they fight together for King Harald Fairhair of Norway.