Helmogog, Emperor of Silk & Fang

"A million million eyes watch you, and appraise you as food. I would have fed you to my favored children, and watch them grow strong on your flesh, but now? After all this? I think I will keep you alive. I will imprison you in webs and have you watch. You will bear witness to the return of the Arachnine."

Helmogog, speaking to the Order of the Argent as they confront him in his Stygian Web

Helmogog was a massive spider-like creature who claimed to be the ruler of all arachnid-kind, and imbued such creatures with a heightened level of intelligence and malice. Helmogog dwelt in a demiplane of his own construction called the Stygian Web, the only known entrance to which was at the bottom of Taratask in the Unterrealm. 
The origins of Helmogog are unknown but sermons from the leader of the Helmogog-sworn Drow, the Ilharess Nylindara, make mention of Helmogog being amongst a race that was "cast aside" by the gods after being "ensared in their machinations". 
In the depths of the Stygian Web the Order of the Argent discovered a temple to Helmogog that served as the narthex to the heart of the web. In this temple, the party discovered numerous murals, statues, and bas relief sculptures depicting their Emperor. Notably amongst these images was that of Helmogog seeming to take a symbolic green flame from a feminine elf-like figure, who appeared to be purposefully defaced. The identiy of this figure is unknown.
Helmogog seemed to possess some form of unknown arcane ability that manifested in the enchanted silks produced by himself and his three lieutenants: the Gateweaver, the Swordweaver, and the Shieldweaver. He also possessed the ability to grant incredible power to his favored followers, physically changing their appearance and granting them a similar form of magic. Helmogog was able to percieve through these Chosen, and upon death he could assumed direct control of their bodies and through which speak. He seemed to relish in taunting and threatening the party when he did so.
Helmogog and his lieutenants were ultimately defeated in the Stygian Web by the Order of the Argent. The death of Helmogog destabilized the demiplane he created, and the collapse of which shunted the party back to the surface of the Realm.