Long ago, the Drow were a society of Elves living on Orrian. But lusting for power and seeking to subjugate their enemies, they turned to Arachne, the cruel goddess of Spiders, who transformed them into creatures that hide in the shadows. Their society became even more ruthless under Arachne's influence as they sought to wipe out other races. Also due to Arachne, they became a fiercely matriarchal society and set procreation as their number one purpose. Eventually, the other races of Orrian banded together to smash the forces of the Drow. The survivors scattered and fled underground.
Today, most of the Drow continue to follow the cold blooded teachings of their mother goddess and the surface dwellers look upon them with disdain for good reason. But there are always exceptions and oddities.