Thalnus Cozzereln is a bulky, broad-backed gnoll with coarse brown fur threaded unevenly with grey, especially along his jaw, shoulders, and forearms. His brown eyes have a steady, appraising look, and one ear has a ragged patch where the fur never grew back. He moves with a delver's careful economy: shoulders turned through narrow doors, weight tested before each step, then a sudden, heavy burst when he commits. He smells distinctly of wet stone, old leather, and the bitter resin he rubs into his boots; he knows about the resin, but insists the rest is just 'the smell of work.' Unexpectedly, he carries a tiny folding paper theatre and repairs its painted scenery with meticulous patience.

Thalnus is dry-witted and stubborn, but his humor is less a shield than a way to keep panic from taking charge. Around strangers he is guarded and exacting; around novices he becomes unexpectedly protective, though he shows it by correcting their knots and checking their boots. When relaxed, he is fond of small practical jokes. When afraid, he turns brisk and bossy. When someone is grieving, the jokes stop and he will sit nearby without demanding conversation.

Thalnus spent four decades delving for salvage, old roads, and lost settlements with a close-knit crew called Hedd's Last Shift, named for a mine foreman whose post vanished generations ago. He joined young, eager to prove that a gnoll could be trusted with more than the dangerous work at the front. His first partner, Brakka, taught him to read stone by sound and to leave a route marker even when the crew was in a hurry. During a collapse in the drowned tunnels beneath Vask, Thalnus heard a second fall coming and ordered the crew back. He disobeyed his own order to retrieve the crew's trapped medic, Jori, and came out carrying him while the others escaped. Jori survived, but the rescue cost the crew its contract and Thalnus his hearing in one ear for several weeks. Years later, on a different expedition, Thalnus walked away from his last crew in the middle of a job. He will not say why. He now lives above a shuttered rope-maker's shop, maintaining old route maps and taking occasional work guiding people through places that have already tried to kill him. He still exchanges blunt letters with Brakka, who thinks he should return to the tunnels, and quietly sends money to Jori's daughter.