Encyclopedia Daemonica is a collection of Doom related fan fiction written by Lyubomir O. Ivanov. A quote from the document itself:
"What you will see is analysis of the fictional world – its plot, components, characters, events, and secrets. Every nuance of that world will be presented with creative background and story, in my attempt to fill in the holes of the Doom world, explain its mysteries, follow the path of its processes, and achieve cohesion and solidity of the fictional universe of the games from the "Doom" cycle. This is expressed in 66 pages of Doom lore."