|Aliases||The Bone Master, the Wormgod, The Worm That Walks|
|Portfolio||Worms, Creation and Mastery over the Undead|
|Domains||Corruption, Death, Destruction, Evil (Dragon Mag writeup), Death, Evil, Pestilence (Living Greyhawk writeup)|
|Home Plane||Prime Material Plane (Oerth)|
|Worshippers||Necromancers, Undead, Worms that Walk, Avolakias, Ulgurstastas, and other worm-like monsters.|
|Favoured Weapon||Mace of Kyuss (Mace)|
Kyuss is a demigod of the undead in the Dungeons & Dragons Greyhawk setting. He's also known as the Bone Master and The Worm That Walks. Not just a Worm That Walks, but The Worm That Walks, as he takes the form of a gigantic humanoid mass of worms and all other Worms That Walk are just smaller imitations of him. Did we mention he likes worms?
Kyuss came to our notice by way of Michael McDonald's Sons of Kyuss, a monster from the first edition Fiend Folio. They are walking, worm-filled undead that attempt to burrow their worms into someone else's living tissue. Being among the few monsters in that book as didn't suck, and in fact rocked, they got their father a metal band named after him. They are Spawn of Kyuss from the 3rd Edition Monster Manual II on, because gender equality (in being horrifically disgusting).
Kyuss's faithful believe that life is obscene, death offers only nothingness, and that undeath is the only worthwhile goal. Followers of Kyuss are committed to creating undead wherever they can; whilst they are permitted to control them if necessary, they are encouraged to set their creations free when they have no further use for them. Undead are sacred to Kyuss, and his followers are forbidden from destroying them except in self-defense.
Before his elevation to demigod, Kyuss was a priest of Nerull who sacrificed every last one of his unsuspecting friends, family, and followers in a spectacular and wormy ritual to please his patron god. Unfortunately for Cleric Kyuss, his reward for having himself and everyone he knew consumed alive by flesh-boring maggots was to be bound into a stone obelisk and abandoned at the bottom of a deep, dark, worm-filled fissure (just as planned), because it turns out evil gods don't like having their authority challenged by their clergy. Whilst inconvenient, this hasn't stopped Kyuss getting Dracolich and vampire silver dragon followers, fashioning whole new types of wormy undead to fill out monster manuals, and creating the Ebon Triad as a front for his cult--pissing off almost every evil god of significance in the Greyhawk pantheon.
Kyuss is also worshiped by a race of Aberrations called Avolakias. He also is the creator of a bunch of giant undead tentacled maggots with the ability to with people they swallow into skeletons called Ulgurstastas. He's the cover model for the 3e book Elder Evils, and appears as one of the nine Evils inside. In that adventure, a Worm That Walks cultist is trying to free Kyuss from his obelisk by destroying it with a black hole created by putting a Sphere of Annihilation, pilfered from the Tomb of Horrors, into a Well of Many Worlds (even though this would also destroy the universe without divine intervention), in the hope that Kyuss will either turn him back into a human as a reward, or grant him the sweet release of death.