The 666 Layers of The Abyss
Demons in D&D have long been one of my favorite villains to pit against PCs. As such, I have slowly developed and altered the baseline D&D cosmology for demonkind to reflect Greyhawk's vast involvement with demons.
Portions of these entries were inspired by the Gord the Rogue novels Gary Gygax wrote (both while with TSR and after his departure), as well as from the AD&D game ran by my good and dear friend, Allen Ruch, while we both attended Penn State University.
Excerpts from The Demonomicon Of Iggwilv
I started this series of articles in conjunction with the late-August 2001 launch of the Greyhawk fan-site Canonfire!, and have sporadically added to the series as time passes.
The Lower Planes
General Demonic Information
Unique Demons (Lords, Princes, etc.)