“Lolth is the chaotic evil god of shadow, lies, and spiders. Scheming and treachery are her commands, and her priests are a constant force of disruption in the otherwise stable society of the evil drow. Though she is properly a god and not a demon, she is called Demon Queen of Spiders. She demands that her followers: (1) Do whatever it takes to gain and hold power. (2) Rely on stealth and slander in preference to outright confrontation. (3) Seek the death of elves and eladrin at every opportunity.” — from Rules Compendium, pg. 50

Further information on Lolth may be found here, here, and here.