Deag Grav

Deag Grav is a Hell Priest of the Blood Temple in the legion of Hell and a creator of the Well.

Background
Originally a lowly demon, he created a scheme to ensure total victory over the realm of the Wraith by making false promise to a Night Sentinel member that he would resurrect his fallen son in exchange for his help in enabling him and his cabal to get close the Wraith. Once the treacherous Sentinel did his job, the Hell Priest and his cabal utilized the Wraith's own essence to create the Well that gave Hell the advantage in the war and finally absorbed the dimension of the Night Sentinels. In the end, Deag and his hellish cohorts didn't give their promise to the Sentinel that helped them by resurrecting his son in the form of a demon, highly suggested to have become the Icon of Sin itself. Deag Grav's fate is still unknown but it can be assumed that he was promoted to demon lord because of his achievement.

Trivia

 * Deag Grav is the only named non-boss demon in the Doom series.