The Age of Worms
A mortal tyrant from over 1,000 years ago, in Rift Canyon who ruled over the city of Kuluth-Mar far to the south. Created dozens of new kinds of undead and amassed huge legion of creatures. Undead dragon stood at his side as the general of his force. He is spoken of in ancient prophecies as being the “Harbinger of the Age of Worms.”
Kyuss was originally a mortal of the ancient Flan kingdom of Sulm, which once stood where the Bright Desert now lies. A priest of Nerull, his mastery of the undead supposedly led his master to grant him divine status, but he is still not a “known” god or a worshipped god (per Allustan), though there is much confusion on that point. Apparently, he was imprisoned at the very moment he achieved apotheosis, bound by an obsidian ring inside a trapezoidal obsidian monolith atop a giant spire in Kuluth-Mar. When the party traveled to Kuluth-Mar in Fireseek, CY 596, they had a vision at the spire of a giant red dragon ripping the monolith from the apex of the spire and carrying it off to the northwest, but the when and why of that action is unknown. Moreover, Scar-Eater identified the red dragon as Dragotha.
His best known (and apparently the weakest) creations are the Spawn of Kyuss. His giant undead vermin creations are collectively known as the Hounds of Kyuss. Allustan has theorized that perhaps he is in league with the Cult of the Ebon Triad.