The Thenns hold a hidden valley in the Frostfangs and set themselves apart from the free folk's usual scorn for lords and laws, obeying a hereditary Magnar — a title meaning simply "lord" in the Old Tongue — with a discipline other wildling war-bands notably lack. They speak the Old Tongue as everyday speech rather than the Common Tongue most free folk south of them have adopted, and hold to their claim of unbroken First Men blood more insistently than the record can independently confirm.
Styr, Magnar of Thenn in Mance Rayder's day, refused to join the King-beyond-the-Wall's muster until Mance had beaten him in battle three times over — a phrase in which the maesters allow "convinced" to do a great deal of quiet work — after which Thenn spearmen and archers became some of the most feared troops in Mance's assembled host.
Styr led the Thenn assault that breached Castle Black's stair during the Night's Watch's darkest hour, and died there when the stair and the ice above it came down on his own men. The Thenns who survived that rout ended the war improbably at peace, sworn to the Watch under a young Magnar named Sigorn rather than continuing the fight that had killed his father.