The Ulfhednar (singular, Ulfhedinn) are mentioned in Vatnsdœla and Hrafnsmál saga, and in Völsunga saga, they were said to cover themselves with a wolf skin when entering combat. The Ulfhednar were defined as Odin's elite warriors, with the wolf skin and a spear as their most characteristic profile.
The poem Haraldskvæði (part of Hrafnsmál) defines them thus:
I will speak of the berserkers, the blood tasters,
Those fearless heroes, how did they treat
Those who wade in battle?
Wolf skin they call them.
They carry bloody shields.
Red-tipped are their spears when they march.
They form a tight group, closing ranks.
The prince, in his wisdom, trusts them,
In those who cut the enemy's shields.
In Heimskringla and Grettir's Saga, they are also called Úlfhéðnar. Harald I of Norway, unifier of the kingdom, appears accompanied by them in his offensives, "they went without chain mail and acted like rabid dogs and wolves", which caused bewilderment and collapse in the ranks of the opponents.
They were marginalized by society as madmen, and a legend that ran through the Nordic countries told that they turned into werewolves, which caused them to be more feared and secluded, already in Christianity, as possessed by the devil.
The belief in lycanthropy is attested in the Volsunga saga, where Sigmund and his son Sinfjotli growled and howled like wolves in their fights.