Baalgar

Baalgar demon is a type of large shadow lord in the hiearchy of hell.

Doom 2016
Petrified remains of a Baalgar was brought back from Hell during one of the Lazarus Hell tethering expeditions (2143) and turned into a Cyber Demon, through a symbiotic mix of a the Baalgar remains and a Argent Accumulator..

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 any cybernetic modifications.