Berserkers were Norse warriors who are reported in the Old Norse literature to have fought in a nearly uncontrollable, trace-like fury, a characteristic which later gave rise to the English word berserk. Berserkers are attested in numerous Old Norse sources. Most historians believe that berserkers worked themselves into a rage before battle, but some think that they might have consumed drugged foods. There are a few who suggest that they were just raging madmen.
The Úlfhéðnar, mentioned in the Vatnsdæla saga, Haraldskvæði, and the Völsunga saga, were said to wear the pelt of a wolf when they entered battle. Úlfhéðnar are sometimes described as Odin's special warriors, with the pelt from a wolf and a spear as distinguishing features.