Demonic Trooper

The Demonic Trooper, sometimes called Demon Soldier or Soldier of Immora, is a new monster introduced in the second downloadable content (DLC) expansion, The Ancient Gods: Part 2, for the single-player campaign of Doom Eternal. They are the warrior caste of Immora, defending it and its inhabitants from external threats while awaiting the return of their leader, Davoth. When he returns, they defend the city while the Doom Slayer and the Night Sentinels invade it.

Unlike the rest of the inhabitants of Hell, the Demonic Troopers retain their original forms through regular infusions of infernal energy, which also grants them a certain form of biological immortality. Unfortunately for them, this does not prevent them from dying in battle.

Codex
''Immora's warrior caste defends the ancient city, keeping watch over the walls since the betrayal of their creator millennia ago. The imperial guard of Davoth remains an honored position amongst the citizens of Immora, wielding armor and weapons forged in the fires of hate and suffering. Their loyalty and devotion to Davoth is unwavering, having waited eons for the return of their rightful leader.''

In-game
Despite wearing full armor and their reputation as the personal guard of Immora, Demonic Troopers are among the weakest enemies in not only the entire game, but the entire series. Their energy shots are slow and deal little damage. They cannot be chainsawed or glory killed, likely due to lacking any real death animations - to compensate, they will always drop some ammunition when killed.

Trivia

 * The Demonic Trooper's armor is based on one of the player's options from the multiplayer mode of DOOM. Similarly, their rifle appears to be the Reaper. Their general appearance and status as elite warriors who nonetheless get slaughtered en masse gives them similarities to the Elite Guards of the UAC's Mars facility in the same game.
 * Due to their use of Hell Energy to prevent their bodies and minds from degrading like the rest of Hell's residents, Demonic Troopers are probably the closest equivalent to basic human enemies in the entire bestiary of Doom Eternal.