In the time before the First Demon Scourge of Boletaria, the ancient Burrowers are the ones who dug out Stonefang Tunnel, the elaborate Tunnel City below the smithing grounds, and created the Temple of the Dragon God at the base of the mine. Unlike the current Excavators (the Burrowers descendents who mine their ancestors tunnels for ore), the Burrowers were led by a King.
The Burrowers were pagans who believed the huge dragon skeleton at the base of the mine was a God which caused the bones of dragons to become the flaming ore dragonstone. So worried were they that the Dragon God would be reborn that they molded an elaborate temple to both appease and seal in the Dragon God. As an added precaution the Burrowers constructed two large magically enchanted harpoon guns on either side of the molten pit and forged the Dragon Bone Smasher, a weapon capable of slaying dragons by crushing their bones.
Also sealed in with the Dragon God was an ancient fire Demon. The Demon may refer to Flamelurker or it may just be the Burrowers' explanation for the unseen force that caused rock to become molten lava.