A Drider is an aberration that was formerly a drow (dark elf). Driders are centaur-like creatures, appearing as drow from the waist up, with their lower portions replaced by the abdomen and legs of immense spiders. They are most commonly found in the Underdark.
Only high-level priestesses in good standing with Lolth are able to initiate the transformation of a dark elf into a drider. This transformation is very painful, and lasts at least 12 hours. Driders develop a poisonous bite. Their digestion changes and they must drink blood of living creatures for sustenance. Driders still maintain the spells and special abilities they had developed as a drow. A Drider can be any character class. They retain intelligence and memories. This usually makes them bitter, spiteful creatures. Some hunt for magic powerful enough to undo the transformation.
Driders play many roles in drow society. The dark elves both fear and are revolted by driders. After transformation, they are usually pushed to the wild area around a drow city. Driders are usually found in company with tiny, huge and giant spiders. Driders speak Common, Elvish, and Undercommon and of course Drow. Driders are almost always Chaotic Evil.
Originally a punishment. (mostly on males) Some Drow have come to see Driders as a blessing from Lolth taking on a form that resembles the spider queen herself.