Ashlar was, still is, a stone carver and sculptor. Statues, collumns, restoration, his workshop always full of pieces and stones of all kind. He used to dive deep in the dungeons to get the best materials for his customers. It was on one of his travels the accident happened. Trying to escape hounds, his hoof lost it's footing and he fell into lava. How did he survive, he doesn't know. He's not even sure he didn't actually die there. But he woke up in the dungeon, a towering stone creature looming over his wretched body. Fear washed over him before he realised it's intentions weren't hostile. His second realisation took longer to settle in. His front legs. Where once were golden brown limbs, now were grey, rocky legs.
If he survived his death, he is now left with magic infused stone replacements of parts too damaged to be healed (everything grey and and black is stone and obsidian). If this lets him continue his work and live mostly a normal life, he is extremely stiff. He doesn't leave on expeditions alone anymore.