Dark Lord

The Nameless One, also called the Dark Lord and the Lord of the Fourth Age, is the unseen ruler of Hell. His lieutenants are the Archdemons, who enforce his will unquestioningly.

History
While the Nameless One has yet to appear directly, it is believed that he may have been the demonic voice that first contacted Olivia Pierce with the offer to ease her pain and is later heard threatening her over her failure to keep the Doom Slayer from being reawakened, and repeatedly urges the demons to oppose the Doom Slayer during various points in Doom (2016). In Doom Eternal, it is also stated that he was the one who negotiated Hell's alliance with the Maykrs.

During the events of The Ancient Gods, Part One, the Slayer retrieves the Dark Lord's life sphere and brings it to Urdak in order to force him to take a physical form- should he be killed, every demon outside of Hell itself will be immediately annihilated. Much to the Slayer's surprise, it is revealed that the Dark Lord is not a king so much as the most powerful warrior in the Dark Realms- and is in fact a parallel version of the Slayer himself.