Lolth

Lolth, the (Demon) Queen of Spiders, is the goddess of the Drow, of spiders and of chaos.

Once a member of the Elven pantheon, the Seldarine, and named Araunshee, Lolth betrayed the Seldarine out of growing malice, discontent, and lust for power. She betrayed her husband, the chief elven God Corellon Larethian to his enemy, the Orc God Gruumsh and tried to help the destruction of the Seldarine. When she failed, Lolth fled to the Demonweb Pits and led her chosen race, the Drow, into the Underdark, becoming a twisted and cruel goddess.

Lolth would soon trick her own grandson into absorbing the essence of a demon lord to corrupt him into serving Lolth as her champion forever. Lolth had the Drow establish a society absolutely built on sadism and backstabbing, solely for her own pleasure, with cruel edicts consisting of demands for the sacrifice of every newborn male child at birth and demands for her priestesses to carve out the hearts of males they grow too fond of.

What sets Lolth apart from other evil Gods is that she cares nothing for her race or her worshipers, viewing them as merely tools for power. For her own amusement, she will capriciously withhold her favor from loyal Drow just for the pleasure of seeing them die. Lolth has nothing less than genocidal fury towards all surface elves and routinely directs her followers to murder them. After becoming more powerful, Lolth proceeded to purge the Drow pantheon of other deities, ending her victory by destroying her own daughter, Eilistraee with savage glee.