Duergar

Also know as known as gray dwarves or dark dwarves, duergar are a subterranean subrace of dwarf. They are known to dwell in the Underdark, often near volcanoes. Their kinship to other dwarven sub-races could be compared to that of the drow to surface elf. Slightly smaller than normal dwarves, they have a magical ability grow to a large size, and have grayish-black skin and white hair.

It is believed that they became so through millennia of slavery under illithid. That slavery was thrown off long ago, though some particularly corrupt duergar are known to still work with mindflayers, often in wildspace.