Hell Knight/Doom 3

The Hell Knight in Doom 3 is huge, very muscular and heavy. An in-game examination of its spine indicates it has a massive skeleton. It has no visible nose. Its ears resemble deformed human ears, fused to the sides of its head, which makes them look almost like holes. Its obscure eyes are very small and black, located on the sides of the head just above the mouth. It is easily the largest non-boss enemy in the game. Assuming the Marine is 6 feet (180cm) tall, the Hell Knight stands about 10 feet (3 metres) tall.

In Hell, Hell Knights show a different appearance than those in Mars. Their skin is greyish-green. Parts such as it's mouth, upper chest, hands, and feet are red, possibly soaked with blood. They are covered with scars and demonic runes, and have a pentagram on their foreheads.

While the classic Hell Knight has horns and hooves, being meant to resemble a beastman or goatman or minotaur, the Doom 3 Hell Knight somewhat resembles a huge muscular skeleton. The head of the Doom 3 incarnation of the Knight is somewhat similar to the Shambler (an owl bear-like creature) from the first Quake.

Two of these massive monsters make their introduction in a cutscene (obviously mirroring the first two Barons of Hell's debut as "bosses" of Doom's first episode) in which the marine arrives at a huge laboratory room where he witnesses the portal to Hell being opened under Dr. Betruger's supervision. A biosuit-clad scientist emerges from it, followed by a huge Hell Knight right behind him. The scientist pleads for his life, but the Knight grabs and throws him violently against one of the portal's generators, presumably killing him; a second Hell Knight comes out from the portal and then both monsters charge towards the marine.

Combat Characteristics
The Hell Knight's attacks are similar to those of the Imp's: it throws fireballs at long range and substitutes to clawing attacks at close range, but it lacks sudden leaps and it's clawing attacks are much slower, which gives the player the time to dodge. However, it has a biting attack, which gives it a farther reach, and it throws green energy balls that are much larger, more powerful, and that have a wider area of effect, with larger splash damage, making them more dangerous in closed space, though they are easier to dodge as the Hell Knight's height means they are launched from farther up, making it possible to literally run under them.

The Doom 3 Hell Knight is actually tougher than the original Hell Knight, having roughly as many hitpoints as the original Baron; the Doom 3 Hell Knight takes six direct rocket hits to kill, while the old Baron usually took five or six rockets (depending on the random damage rolls). It is probably for this reason that there is no Baron of Hell in Doom 3; the Hell Knight fills the role. Particularly, the Doom 3 Hell Knight is the reinterpretation of the original Baron of Hell.

Tactical analysis
When facing a Hell Knight, it is strongly recommended to use the Soul Cube or the BFG if it is necessary to take them down quickly, for they can absorb large amounts of damage. But if the situation permits, the rocket launcher, plasma gun, chaingun and even the shotgun are effective enough. It is a very bad idea to retreat from one when he's about to throw a energy ball as its splash damage radius is rather large and it is recommended to avoid being in close proximity to walls or other solid objects. The chainsaw, while powerful, is not a good choice against a Hell Knight.

Hell Knights hang tough, and it can take 100 rounds or more of Machine Gun fire (almost 2 full magazines) or close to a full magazine of Chaingun or Plasma Rifle fire to kill one (somewhat less if you can score consistent headshots, which is relatively easy due to the Hell Knight's slow speed and huge head). The shotgun is reasonably effective against Hell Knights, and can kill one with a handful of shots, especially if aiming at the head. However, this tactic requires the player to close in at point-blank ranges and render themselves vulnerable to the extremely damaging melee attacks of the Hell Knight. The Grabber is a relatively effective weapon, however it requires 5 direct volleys from and back at the Hell Knight to vanquish it. The super shotgun is also relatively effective, provided the player has sufficient space to keep dodging, firing and reloading.

In some levels like Hell, you can circle around it with your shotgun to save ammo for stronger weapons, due to the infinite stamina you have, or you can use adrenaline to help you in normal levels.

Although Hell Knights can survive significant damage and have powerful attacks, their attack rate and speed are quite slow, and are normally fairly easy to dodge. However, they can be very dangerous if they manage to pin you inside an enclosed space or narrow corridor where you do not have sufficient room to effectively dodge their attacks.

UAC Research Notes
These notes can be downloaded to the Player's PDA during the course of the game:

Specimen 31 - Hellknight (partial)

''The cranial mass of this bipedal specimen indicates that it is one of the largest creatures inhabiting the site. Overpowering its prey with sheer might, the Hellknight is one of the most ferocious predators known to our researchers. Like the imp, this creature is able to defend itself at long-range with thrown plasma projectiles.''

Doom Resurrection
The Hell knight is a boss in Doom Resurrection in the fourth chapter, inside the delta labs. Its only attack is to throw green energy balls at you which can cause quite a bit of damage. They can be dodged like a usual Imp's energy ball. After draining its energy bar, it will push you into the stargate(?), sending you to hell.

Trivia

 * The first Hell Knight's appearance was in Delta Labs 4. The portal to hell activates, and two Hell Knights emerge. This is reminiscent of the first bosses in the original Doom, where the player must defeat a pair of Barons of Hell at the end of Knee-Deep in the Dead.
 * The first two Hell Knights fought at the end of Delta Labs 4 have noticeably more health than the regular Hell Knights fought later in the game. Each one has about 1400 health, compared to 900 health for a standard Hell Knight. This makes the two of them something of a boss encounter, similar to the two Barons of Hell from the end of the first episode of the original Doom.
 * The Hell Knight is often said to be the scariest enemy in the game for many reasons. The beast is one of the tallest enemies in the game, it has an unsettling visage and growl, is a powerful enemy and makes the screen shake when it walks.
 * Interestingly, if one can use the noclip cheat, a stream of saliva can be seen running from the Hell Knight's mouth.