Deag Grav is a Hell Priest and one of three coordinating the demonic invasion of Earth at the behest of the Khan Maykr. He is first mentioned in Doom (2016), and appears as the secondary antagonist in Doom Eternal.
Originally a priest of the Order Deag, Grav was present along with Ranak when the Night Sentinels brought in a stranger they had found in the grounds of Sentinel Prime. As was customary for the Argenta, the man was sent to the Arena to battle against others, proving more resilient and relentless despite his maddened ravings about demons. Grav praised the stranger's capabilities before the Khan Maykr ordered him to dress his wounds and bring him to her so he could tell them more about the "others" he mentioned.
Along with his fellow priests, Grav was eventually corrupted by his lust for power and Argent Energy, becoming a demonic entity who only sought to ensure the prosperity of the Maykrs at the expense of the worlds under their command. He created a scheme to ensure total victory over the realm of Argent D'Nur by making a deal with a member of the Night Sentinels: Grav would resurrect his fallen son if he gave Grav access to the Wraiths in the Sepulcher of Elements. Once the treacherous Sentinel did his job, the Hell Priest and his cabal siphoned the Wraiths' own essence to the Well that gave Hell the advantage in the war and finally absorbed the dimension of the Night Sentinels. While Grav fulfilled his promise after a fashion, he instead used the heart of the Betrayer's son to resurrect him in the form of the Icon of Sin.
Thereafter, Grav became the overseer of Sentinel Prime, turning the Arena into a bloodsport that pit humans against demons to entertain himself and the populace that remained loyal to the Khan Maykr.
Deag Grav and his fellow Hell Priests oversaw the invasion of Earth at the Khan Maykr's orders. He and Ranak were performing a ritual to accelerate the process when the Doom Slayer arrived and threw the severed head of Deag Nilox at their feet. Grav's threats fell on deaf ears as the Slayer readied his Shotgun, but he and Ranak were teleported to safety by the Khan Maykr.
Grav's location was unknown for a long while, with the Slayer focusing his efforts on killing Deag Ranak before seeking out Samuel Hayden to pinpoint his location: Sentinel Prime. When the Slayer came for him at the Arena, Grav taunted him with the knowledge that spilling "Sentinel holy blood" on sacred ground would cost the Slayer's sovereignty with the Night Sentinels. He then unleashed The Gladiator upon the Slayer, who slew it before claiming the medallion that would render Grav vulnerable. Grav spitefully told the Slayer that killing him will not stop the consumption of Earth before having his head blown off by the Slayer's Super Shotgun. As Grav had warned, his demise made the Night Sentinels hostile to the Slayer, who simply threw the medallion onto Grav's remains before returning to the Fortress of Doom.
Grav was an extremely loyal and fanatical follower of the Khan Maykr, possibly even moreso than his fellow priests, Ranak and Nilox. When facing imminent death at the hands of the Doom Slayer, he showed no indication of fear or remorse. He was also extremely cunning and manipulative, as demonstrated when he tricked Valen into giving the forces of Hell access to the Wraiths.