Duergar

Duergar, also known as Dark Dwarves, are a subterranean subrace of Dwarves that carve out their existance in the Underdark and are akin to surface Dwarves as Drow are to surface Elves.

Duergar Origins
The Duergar were once a settlement of Shield Dwarves in the Dwarven kingdom of Shanatar. The Shield Dwarves that eventually became the Duergar lived in certain strongholds that fell under attack of Mind Flayers, or Illithids, and were captured. During their captivity, which lasted for generations, the Illithids performed many cruel and unusual experiments on the dwarves. Eventually, the Dwarves rose up against their captors and gained their freedom from the Mind Flayers. Now the Duergar inhabit the Underdark and have been left as cruel and evil as their captors and quite withdrawn from their experiences.

Duergar Appearance
Like the Drow, Duergar have a gray to black skin tone and white to gray hair. They are a good deal thinner than surface dwarves and have extreme expressions. No Duergar has hair on his or her head, but the males do grow beards.

In the chance that an adventurer wanders across a Duergar on the surface, that adventurer is likely to notice facial and arm tattoos that mark the dwarf as a traitor to Duergar society.