The Gladiator

The Gladiator is a mysterious demon shown in the story trailer of doom eternal and on artwork for doom and is presumably a boss.

Appearance
The Gladiator has a large body similar to the classic Hell Knight with the addition of some body armor, however its head resembles a classic baron of hell 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. BUT, there is actaully a way to kill him, which involves destroying his shield, which is stated to contain the tormented soul of its master.