Duregar

The grey dwarves or Duregar are never found in the Overworld unless they are a member of the raiding parties that leave the Underdark in search of slaves.
The primary duregar societies are based around War Leaders and a slavery driven society. These war bands often work with and supply slaves to the other societies within the Underdark, like the Followers of Lloth and Mind Flayers.
It is incredibly rare for a Duregar to grow up separate from a war band, though there are very few and scattered smaller settlements of Duregar who exist in a much more sedentary and self sustaining manner. These often do not rely upon slavery and much more closely resemble the smaller towns of hill dwarves from the Overworld.