They are the Zellish faction with the longest history in the North, having been fighting a perennial feud with the Northmen since before the beginning of recorded time.
The Branded Zells get their name from their brands. Instead of the more common tattoos, they sear marks into their flesh with hot irons. The more brands the Zell has, the more people he has killed. They are famous for their food (including the legendary Bork) and for their skill at arms with their hooked clubs.
Ironically, despite having a horrible reputation among their racial fellows, the Branded Zells have a pretty good reputation in the Genosian world. Their Bork delicacies and shagreen coats are greatly coveted, and such was their influence that at one time, a daughter of the tribe married a Krajini prince, and the royal family of the Krajina was Zellish for many generations. This has had consequences, as Queen Dahaka the Black has serious rage issues, but it did set a precedent for friendly relations between the Zells and the Sliver Kingdoms.
Each of the Branded Zells make their own club. Sort of a right of passage thing. Of course, they have access to steel, and often use these to reinforce their clubs, or to add spikes or small blades.
The current leader of the Branded Zells. In the north, Shahaka Andresilja is pretty much universally despised, even among the non-Pagan northmen. She and her brood have killed millions of people over the years, and their cruelty is the stuff of legends. Villages even in the civilized north of the Thanemarch and Svitgard might be safe on paper, but in practice, the Branded Zells frequently pick off isolated settlements, to fill out their quotas and to remind the northmen that they'll never truly be safe so long as Andresilja lives.
She's an old Zell, who has some sort of beef with the men of the north that she has carried with her for centuries. She had a large hand in engineering the Ruvian Church's bounty on pagans, and her tribe have been the prime collectors ever since.
Something else she is known for is having beautiful daughters. One married into the royal family of the Krajina, resulting in several generations of Zellish royalty in the Slivers. Others have married into noble families across Vosca.
What makes the daughters of some crazy Zell so attractive? They're said to be charmed. The families that marry into the line all seem to enjoy periods of sudden success and ascendancy. Many credit this to some sort of holy work that Shahaka has done to earn the good grace of Genosus. Others suspect witchcraft.