Linden

Linden is a being of unknown race or origin. While appearing human and male, his immense knowledge of almost everything means it's unlikely he is a being of any type the  Questers  have thus far encountered.

Alternate Universe
The Questers met Linden in the AU when Mirror Bran used The Gunslinger's book, brought to the AU by The Green Kitsune, to runically summon him, with the intention to use Linden's vast stores of knowledge as a resource to prevent Ragnarok. Upon his invocation, Linden expressed shock and anger before the Questers were able to assure him they were allied with Odin. When he was satisfied with their proof, he agreed to join them. Shortly afterward, he corrected the mistaken assumption that the Shadow was multiple entities and informed them that Exlon was only triune in order to hide from the Shadow.