Rune Priest
Rune Priest are fucking Librarians of the Space Corgis and their existence is one of the most infuriating for those who despise the fucking yiffers. Part of the reason why is because of the notion that the closet furries have a particular hate boner for psykers, especially the Thousand Sons, and are known to treat psykers with suspicion and mistrust. As you can imagine, during the burning of Prospero, Magnus pretty much went, "What the absolute Fuck on Tizca's Tip, Russ! You hate our people for who we are and yet you yourself use psykers in your ranks!?", to which Leman promptly rebutted, "But these aren't psykers you see....they're....shamans, YES! Anyways...FUCK YOU NEEEEEEEEERRRRRDDDDD!" (Yeah sure, let's just ignore the fact that Thousand Sons were accompanied by ACTUAL LITERAL DEMONS and tapped into their powers constantly and wholeheartedly, while runepriests are/were much, much more reserved. Still hypocrite, sure, but let's not pretend that it's the same thing.)
This blatant hypocrisy has often been the main ammunition for those who hate the Space Wolves. That, and their overall unhealthy lifestyle with their pet wolves.
Anyways, like the Librarians of Codex Chapters, Rune Priests are combatant psykers, using their psychic abilities to aid their brothers on the battlefield; off the battlefield, they are the keepers of the chapter's librarium and store of knowledge. The major difference is that Rune Priests do not believe their psychic abilities are derived from the Warp, but rather from the animistic spirits of their homeworld, Fenris, channeled through totems and runes on their armour, which as you can imagine, is fucking bullshit and is just more excuses for the Wolves to say, "Nuh-uh! Erh Meh Gerd! Des Tertelley Nert Psykers At All!". These traditions are descended from the shamanistic rituals of Fenris's native tribes, and have remained unchanged for countless centuries.
Worst of all, using rituals and tools for channeling psychic powers is the textbook fucking definition of sorcery, so for all their boasting about Maleficarum and Wyrd, Rune Priests are basically as damned as the Chaos Sorcerers they so despise. Worse even, as Chaos Sorcerers at least know what they're doing and what the price and the dangers are.
Rune Priests preserve their Chapter's entire history not in written form, but memorize it in great sagas. A Rune Priest who begins his training as a Skald is usually assigned to a single Great Company where he is taught its tales. With every new Great Year he joins another Company until he has learned the Chapter's full history and can be sent to whichever Rune Priest needs an apprentice.
The basic weapons of the Rune Priests are their psychically charged Runic Weapons. A common power among Rune Priests is the ability to summon storms across the battlefield which can cover the army's advance. Furthermore, they can cast runes which predict the ebb and flow of future events. These runes are usually carved from the bones or teeth of totem animals.
Many Rune Priests are psyber-linked to cyber-ravens, which are known as "Choosers of the Slain" to the Space Wolves. Their link enables them to see through the ravens, eyes and control them, thus allowing them to use them as scouts and messengers.