Ruins of the Old Empire
The duergar were the second race known to inhabit Ammunar, and the first to reach it by following the byways between dimensions. They must have co-existed with the native elves for a while, building their homes under the mountains and gathering their strength, but there are no elven records left from that time and the dwarfs refuse to discuss it.
Suffice to say that they conquered Ammunar’s natives, taking many of them as slaves and driving the rest into the deep forests where they remain today. For 3000 years Deurrack—the Shadow Kingdom—was the power in Ammunar, their unlit fortresses and complexes ramifying for a time before the slow, mysterious decline of their race began.
Strictly speaking, the duergar are just dwarfs, and by far the majority as compared to the pink-skinned ones most other races know well. Their society is confined to vast underground complexes in the high mountains of Ammunar, partly by treaty but largely due to their own preference. There were once many more of them, and it seems that the duergar have lost much knowledge of their own arts as they abandoned many of their halls. These are abandoned, not deserted, for the black dwarfs’ attitude was that if they could not have the cities, that was no reason that anyone else could have them. Apart from the two great halls of the Eladrin assigned by treaty and the more numerous smaller outposts retaken by same, forgotten dwarfish halls have been deliberately salted with insidious traps, and ghosts purpose-made by sacrifice and consumed with bile by their lot. The majority of dwarfs have inky black skins. About one in ten is a deep red instead, but the significance of this is unknown and—as usual—the dwarfs do not talk about it. Their inhabited halls are poorly known, for most are utterly closed to outsiders. Anyone foolish enough to seek entrance is either ignored, or killed out of hand if they seem to be a threat.
Most of what is known dates back to now-abandoned Bdunn, when tightly escorted individuals would sometimes traverse great stone hallways and vast caverns of rock and molten metal to meet with some reluctant duergar official. Even during the days of limited Ilmand-Deurrack interaction, unaccompanied and wandering visitors outside the isolated Alienage were under sentence of death, and there’s no reason to believe that situation has improved since the fall of the Old Empire.
On rare occasion, a human, halfling or (much more rarely) elf will deal with a duergar directly; the black dwarfs sometimes seek to make magical items for the other races for their own peculiar purposes (usually involving a trade of some sort, which turns out to be dire in retrospect).