The duergar are dark dwarves, much in the way that drow are dark elves. Little is known about this secretive race, beyond the fact that they tend to inhabit the Underdark beneath the mountains. They are recognizable by their dark skin and their white hair and beards.
Duergar tend to be extremely distrustful of magic. They also have a tendency to be slavers, preferring to keep goblins as slaves as they are highly expendible and easy to control.