Baalgar

History
A Baalgar demon is a type of large "shadow lord" in the hierarchy of Hell. In DOOM 3 the Cyberdemon may possibly be a Baalgar demon based on the appearance and attributes.

Doom (2016)
The petrified remains of a Baalgar demon were brought back from Hell during one of the Lazarus Hell tethering expeditions (2143) and transformed by the UAC into the formidable Cyberdemon, through a mixture of the Baalgar demon's remains and UAC technology. The implanted technology replaces parts of the body that were destroyed during or after its death, most notably a weapons system entirely replacing its left arm capable of discharging both conventional explosives and the same energy-based attacks utilized by the gun-arms of Possessed Soldiers. The UAC technology is powered and maintained by an Argent Accumulator. A poor choice in design gave the Cyberdemon the ability to activate itself and, after rampaging through the Lazarus Labs installation, the Cyberdemon was confronted and, subsequently, destroyed by the Doom Slayer.

Doom Eternal
A smaller Baalgar demon skull can be seen inside the Cultist Base, frozen into a wall of one of the shafts, and held up by chains. This one doesn't appear to have any evidence of cybernetic modifications. The Tyrants, which take the role of the Cyberdemon in this game, notably don't look anything like the 2016 version of the creature, and thus are NOT Baalgar demons. The Tyrants are actually Harbingers Of Doom. There are no other confirmed Baalgar demons in any other doom game. The most likely demon to be a Baalgar is the Cyberdemon from DOOM 3.

Trivia

 * The term "Baalgar" may be translated in various ways; "Baal" is the semitic word for "Owner" or "Lord", later on "God". "Gar" may be a version of "Gaar", which could mean many things, such as "To rebuke", "Going too far", "Encroach", or even "Neighbor" in modern semitic languages. Therefore the Baalgar would translate to "Lord/God of ###".