Despite resembling small dwarves, duergar do not see them as kin. Legends on how they came to be are conflicting. Duergar believe that derro are descended from a clan of dwarves that were enslaved and demented by mind flayers. Derro themselves tell infinite variations of a story involving two brothers, Diirinka and Diinkarazan, and stealing magical power to escape great evil. Diirinka is their god, though they do nothing to worship him.
Derro flock together to make up for individual weakness and are led by those among them who have been blessed with sorcerous power, known as savants. They tend not to have their own settlements, but rather live in the slums of duergar cities like Gracklstugh.