The Lorekeeper's Tome

The Duergar are the grey dwarves, a sundered branch of the deep-folk who long ago went down into the deepest dark and did not come back the same. Grim, grey-skinned, and bitter, they raise their own holds in the lightless deep below the Iron Hills and regard their sunlit kin as soft traitors to be raided and enslaved. They share the dwarves' skill at stone and steel and none of their warmth, and a party that breaks through into Duergar territory finds the deep-folk's craftsmanship turned wholly to cruelty.