Derro

The Derro are a type of dwarf that live in the Underdark. In the modern day, almost all Derro reside in settlements with their kin, the Duergar. The Duergar use the Derro as slave labour, seeing them as nothing more than vessels through which the Work may be carried out.

History
The oldest legends of the duergar state that the two races were once indistinguishable from one another. Mind flayers infiltrated and took control of a nation of dwarves known as the Derrow, experimenting on them and reducing them to little more than maddened thralls. The illithid commune was eventually defeated by the Duergar and the surviving dwarves freed, but they had long ago succumbed to the insanity. The duergar sought to wipe out the survivors, their induced insanity viewed as a curse that rendered them unsuitable in the Work, but the leader of these survivors, Diirinka, desperately tried to prove that they were still of worth.

Diirinka worked his people to the bone, mining, tunneling and digging without food or rest, and, according to legend, on the third and final day the duergar had allowed him, uncovered a seam of adamantine that had been previously passed over unnoticed.

The Deep-delvers took this as a sign that these dwarves, despite their madness, had a place in the Work. The Grags of the Duergar decreed that the Derro, as they came to be called, were required. As the world itself was tainted by the corruption of chaos, the Derro would act as a buffer against this madness for the pure order of the Work to be formed by the Duergar, who, in their logical perfection, could not fully account for it.

Society
Derro are reasonably widespread and likely to be found in small bands throughout the Underdark. Derro warrens tend to exist in many duergar cities and even some drow settlements; there are rumours of independent derro strongholds in the deepest reaches of the Underdark. Derro scouts and marauders search the areas around their settlements for victims to enslave and torment.

It is very common for derro to devote themselves to some strange quest, such as collecting only certain types of gemstones or slaying as many members of a particular race as possible. This quest is usually seen by the individual to contribute to the Work in some mad way.