The Gladiator

The Gladiator is a demon that debuted in Doom Eternal. It serves as the boss of Sentinel Prime.

Appearance
The Gladiator has a large body similar to the sketch of the classic Hell Knight by Adrian Carmack but with the addition of some body armor. However its head resembles a classic Hell Knight but missing one of its eyes, it wields a shield and mace for weapons.

In The Art of Doom Eternal, it is stated that the Gladiator cannot die, as when his flesh is destroyed, his soul shall wait for his body to rebuild like most demons in folklore, mythology, and in collective religions. There is a way to kill him, however, that involves destroying his shield, which is stated to contain the tormented soul of its master.

Combat Characteristics
It hides behind it's shield to shrug off attacks. When the eyes of the shield flash green, attack. A headshot will stagger it for a Glory Kill, which isn't really a kill, but it involves punching the Gladiator twice, making it drop health points. Do this again and again until you reach his second phase. When the Gladiator's eye flashes, attack. Do it again and prepare for one of the longest glory kills ever.

Trivia

 * The Gladiator's face bears a strong resemblance to the Barons of Hell and Hell Knights from the classic Doom games.
 * As the Gladiator's codex entry suggests that it has been present in Sentinel Prime since the Sentinel Civil War, which seems to have occurred not considerably long after the Doom Slayer's arrival in Argent D'nur (and ergo not too long after Doom 64, which still utilized the classic Hell Noble designs), as well as several Sentinel codex entries depicting the classic design, it is very possible that the Gladiator is indeed an original Hell Knight or Baron of Hell (its coloration suggests Knight, but its size suggests Baron) that has become uniquely powerful.