Lolth - Elven Goddess of Spiders and the Demonweb Pits

Vey'Arill as she was formerly known; Once betrothed to Corellon - Lord of the Elves -  she convinced the primordial elves to give up their mutable forms. Corellon took this as a betrayal and cast all the elves out of Arvendor - essentially the Heaven for Elves. This ended their engagement, but he still regarded her in the Seldarine. She eventually plotted against him and tried to dispatch him several times through various means of manipulation of other deities. The final attempt which she thought to have succeeded was ultimately interrupted by Sehenine the Elven goddess of night. Corellon stripped Vey'Arill of any bit of elven resemblance she had mutating her into a spider with a humanoid torso. A battle between them ensued with Corellon ultimately winning. He threw his blade at her causing her to fall from a suspended position. A portal opened up below her casting her into the Abyssal plane.  
After gathering allies within the Abyss, she eventually abused those relationships and attaining enough followers to regain her status as a worshipped greater deity. Finding a way back to the Material plane, vowing to rule over the underdark, she staked her claim there with her devout followers. 
She also aside from the portfolio of Spider, she carries that of chaos and assassination as well.