Derro

From Syra D&D Wiki

Derros are a crazed race of subterranean humanoids. Their origins are a mystery; they seem to have no real civilization to speak of, living mostly in ancient ruins and caves, and those subjects who have been captured were found to be utterly mad and incapable of rational discourse. They are unique among the various Underdark races in that they are almost universally despised by the other societies that dwell beneath the surface. Some scholars theorize that the ruins they inhabit are in fact those of their progenitors, long-since destroyed by some cataclysmic event, but there is no solid confirmation for this theory. If true, however, then it is clear they have fallen a long way since the days of their ancestors.