Úlfhéðnar are well beyond Berserkir. They are Óðinn's special warriors, and elite Viking forces. They are known to wear a wolf pelt (in contrast to regular Berserkir who wear a bear pelt), and to be inhabited by the spirit of wolves. Úlfhéðnar are capable of performing feats far beyond the abilities of other warriors. Úlfhéðnar are hamrammir (shape shifters). They don't wear a helmet or a mailcoat, bit their shield in a rage prior to each battle, kill enemies with just one blow, and are immune to fire or iron. Úlfhéðnar are exclusively males.
Without Berserkir and Úlfhéðnar as shock troops, King Haraldr hárfagri would have been unsuccessful in his quest to unify Nóregr (Norway). After all, Úlfhéðnar, were not only the best warriors of the time, they were also the most feared.
The Church, however, has always had a unholy fixation on both Víkingar and wolves. So the clergy quickly claimed Úlfhéðnar (and Berserkir as well) were "Heathen Devils". When Eric Hákonarson decided to embrace Christianity, he therefore outlawed Berserkir and of course, Úlfhéðnar as well. With the Christianization of Iceland, Grágás (medieval Icelandic law code which contained a Christian law section) also sentenced Berserkir and Úlfhéðnar to outlawry.
Úlfhéðnar nowadays are still stigmatized. Some of the Úlfhéðnar's traditional skills are seen by western societies as "toxic masculinity", while Úlfhéðnar's spirituality, knowledge, and way of life are often demonized by the church.
Úlfhéðnar today remain indeed super crazy víkingar (really) and modern elite warriors. They are masters of all things Norse. They've got the spirituality, the mental, the physical fitness, the knowledge and the skills (ranging from survival and martial, to healing, or even the ability to reach altered states of consciousness).
Úlfhéðnar are born. Not made. It is therefore a matter of developing underlying potential in the very few males who've got what it takes in their blood, genes, and spirit. These dormant Úlfhéðnar are normally selected during Berserkr training, or within specific military units and special forces, from the best among their peers. Úlfhéðnar can also be identified during any stage of training and developed accordingly as applicable.
Úlfhéðnar are organized into units (Hirðir) made up of twelve guys. Víkingaherr currently has several Úlfhéðnar Hirðir, under the command of Úlfhéðnar Hirð Ein (Unit One). There are also other units not directly related to Víkingaherr and typically associated as well with other special forces.
Úlfhéðnar see wolves as sacred, and as a result, never hunt them, or even take photographs of them. Wolf pelts are gathered from individuals who experience a natural death.
Úlfhéðnar's ássinn is either Óðinn or Þórr (there's a great deal of flexibility for such things). Because, yeah, the christianization attempts on Úlfhéðnar over the last 1,000 years simply miserably failed! This means Úlfhéðnar who die in combat do go to Valhöll, not the Christian "hell"!
BEING A ÚLFHEÐINN
You cannot apply to become a Úlfheðinn. It's in your blood/genes, or it isn't. If we think you've got it in you, we will approach you and bring your skills (ranging from survival and martial, to healing, or even the ability to reach altered states of consciousness), your spirituality, your mental, your physical fitness, and your knowledge up to standards, so you may have a shot at joining a Úlfhéðnar Hirð.