- Zombie: The basic zombie, first found in Mars City Underground. It attacks with a variety of mêlée weapons, including flashlights, wrenches, and its fists. Although there are cosmetic variations—including a mostly headless variation (missing everything above the lower jaw) that is almost immune to headshots—its durability and range of attacks are identical.
- Fat Zombie: A fat zombie that behaves like a basic zombie, first encountered in Mars City the second time around. Unlike the basic zombie, it inflicts more damage with one strike, and can endure more damage. It also moves more quickly when its arms are raised, but is otherwise slower. Some fat zombies wield wrenches that extend their attack range.
- Flaming Zombie: A perpetually ablaze zombie that rushes at the player. According to the book The Making of Doom 3, the game's designers affectionately named this zombie "Bernie". This enemy is also first found in a hallway in Mars City as it rages out of a closet containing an open flame from a damaged pipe.
- Chainsaw Zombie (Sawyer): A burly zombie that wields a chainsaw. It is faster than regular zombies, and laughs maddeningly upon sighting the player. It was dubbed 'Sawyer' by designers. One of them is found wearing a party hat in Delta Labs – Level 4.
- Z-Secs: UAC security personnel that have been possessed and are first seen during the Mars City Underground. They are very common throughout the game, as the facility was full of security teams. As former soldiers, they are better armed and display more sophisticated attacking methods than civilian zombies. A Z-Sec may use a pistol, shotgun, or machine gun. A Z-Sec brandishing a machine gun always wears a full helmet, which conceals its zombified facial features and may sometimes confuse the player into thinking it is an ally. The pistol Z-Sec is the only type that does not usually wear a helmet, and is consequently the only type that sustains extra damage from headshots. A pistol Z-Sec occasionally bears a helmet and shield. The shotgun Z-Sec's weapon has significantly less spread (5°) than the player's shotgun (22°), making it surprisingly accurate. A Z-Sec's presence can be heard by its incomprehensible radio chatter.
- Zombie Commando: A zombified marine that has been physically warped by the powers of Hell, as witnessed in a cutscene where Betruger mutates a live marine. These Commandoes are larger and more muscular than the other zombies. There are two types of Commandoes: one wields a chain gun that inflicts heavy damage; the other rushes and attacks the player with an extending demonically-enhanced tentacle. Commandoes appear to be much more intelligent than standard zombies, being able to speak coherently (Some can be heard saying "You!", "Die!" and "You will die!" in a raspy voice) and perform more complex attacks, as shown in the Tentacle Commandoes' kicks, punches, and lunges. Chaingun Commandoes are able to endure more damage than Tentacle Commandoes. Due to the demonic mutation involved, Commandoes disintegrate after death in the same fashion as normal demons.
In addition to the above, there is also another variant of zombie encountered in the "Hell" level, which is named as "Living Dead" earlier in the game. These zombies have gray skin and lack clothing.
Imps are Hell's cannon fodder, and bedevil the player throughout the game. The Imp is the first enemy to enjoy its own introductory cinematic during the Mars City Underground level. It is humanoid in appearance, with gray skin, 10 small red eyes and bony scales covering its upper arms. It attacks by either launching fireballs in a parabolic path or attempting to slash the player with elongated claws. It can also leap at the player to strike from afar, knocking the player back and causing damage. From time to time, it drops from the ceiling to attack the player, though this behavior is strictly a scripted event and is not independently engaged by the entity's AI once the creature has been spawned in the game world. In the Hell level, Imps use the "branded" skin pattern: pentagrams are seared into their skin at various locales, and their overall skin texture appears burned.
Autopsy examinations, seen on computers screens in autopsy rooms, suggest Imps' and humans' physiology are alike, particularly with regard to the shape of the skull. UAC data files reveal that imps have very good all-around eyesight, even at low light levels.
The Pinky (a.k.a. Pinky Demon, Bull Demon or simply Demon) is a half-mechanical, lumbering beast that attacks with its jaws. It stomps around on four legs; the two rear legs being mechanical in nature. Its top half is hunchbacked and muscular. Demonstrating its power during its first in-game appearance, it completely bends a metal guard rail forward. It then attempts to break its way through a thick metal door, leaving visible dent marks, and then bursts through bullet-proof glass to reach the player. It has quick and damaging attacks, and rushes at the player at a very high speed until either of them is dead.
The designers have explained the unique face of the Pinky demon by describing how it is born: a newborn Pinky's face is buried under thick folds of flesh (that do not, unlike other animals, undergo apoptosis), and the animal must consume itself to breathe and eat.[ ]
It should be noted in some places in the Hell level of Doom 3, the organic half of this demon can be found hanging on meat hooks. The reasons for this are mainly unknown, but some speculate that they could be a food source to the other demons in Hell, but a more logical explanation is that they are awaiting attachment to their mechanical hind legs, or perhaps have died in the operation required to attach them.
In the Doom film, the character of Marcus "Pinky" Pinzerowski, who has a bionic lower body resembling a Pinky's lower body, is mutated into a Pinky near the end of the film.
The Maggot has a similar appearance to the Imp but it is slightly smaller with a greener skin tone. It can stand up and rush at the player. Instead of one head, it has two which both feature orange eyes. Its frame is monkey-like which makes it move on all five of its legs (three on the right side, two on the left). Its back has blade-like parts erected from two large, red, fleshy areas. It also has two long, red tongues (one for each head). Like the Imp, it is capable of crawling on walls and other surfaces, supporting the idea of a possible relation. When the player first encounters Maggots there is a very unfortunate scientist who has been pinned up to the ceiling and has had a pre-death autopsy.
Although the Maggot inflicts little damage with its claw and lacks a ranged attack, it features a swift and powerful leap attack. It is weak compared to other demons of its size, but its speed and ferocity compensate for its relatively low strength.
Despite the name, it does not resemble real maggots in the slightest.
The Trite is a spider-like demon that comprises an upside-down human head (with multiple eyes) with six legs sprouting from the base. Closely examining the back of a Trite reveals a spinal cord appearing from the back of the head and curling down to the lower area of the body. Like a Lost Soul, the Trite may be of human origin, possibly a demonic mutation of a human head, and do not dissolve into embers like the other demons do when it is slain.
The Trite attacks with leaping bites, and though it is quite weak individually, it tends to appear in large groups. It normally appears from cracks and holes behind or beside a player, or it rappels down from the ceiling using its webbing.
The Tick resembles the Trite, but has a smoother head. The Tick can be found in only two places in the game (in the side hallway adjacent to Delta Lab level 4), and also in the expansion pack, Doom 3: Resurrection of Evil (in the last level of hell going down the cave stairs). Ticks are extremely weak, and even two pistol shots are enough to destroy one. The Tick's "head" more obviously resembles a human female, and in particular the Vagary's head.
A Lost Soul is a flying human head, propelled by mechanical jets placed in the rear of the skull. Though its face is obviously human, it has long metallic needle-teeth that are used in its method of attack. Like other weaker enemies of the game, it appears in packs.
Lost Souls fly quite quickly, and it performs a lunge to deliver an attack. Tears can be seen streaming down the faces of Lost Souls. A memorable, gruesome cutscene in the game shows a female UAC employee being transformed into one; her entire head and spinal column are torn from her body, at which point the head jettisons the spine. This cutscene is seen in the EnPro level.
In several cutscenes in Doom 3, flying ghost-like skulls fly about possessing humans. These skulls closely resemble the Lost Souls from the classic Doom games. The design of Lost Souls was modified several times between Doom 3's E³ 2001 presentation and its release in 2004.
The Cherub is a small demon. Its lower half is an insect's abdomen and its back has insect-like wings. The Cherub's upper half features two arms that end in clawed hands and has a little baby's torso. Its eyes are pale and devoid of pupils. Whenever it flies around, it makes a buzzing noise and when it attacks, it emits a harsh screech. Sometimes, just before entering a room or area with Cherubs, the player may hear a disturbing sound, emitted by the Cherubs, which sounds like an infant making a gagging sound.
The Cherub can only perform mêlée attacks, which consist of leaping at its enemies with a force that can knock them back, and slashing with its claws. It has very limited durability, but its agility and small size make it a harder target. As a result of its top half resembling that of a human infant's, the Cherub is considered to be quite disturbing in appearance.
The Cacodemon is an organic flying demon that is roughly spherical in appearance, resembling a large, inflated demonic head that slowly floats across areas. It has several eyes and a large mouth filled with multiple rows of teeth, similar to a shark.
Though the Cacodemon does attack with these teeth at close range, its main attack is a long-range "ball lightning" fireball spat from its mouth. Its fireballs do as much damage as an Imp's, but they differ in terms of trajectory, visual appearance, and larger splash radius (see chart). Interestingly, it is often fairly easy for the player to destroy Cacodemon ball lightning in mid-flight (as opposed to an Imp, Hell Knight, or Vulgar, whose arcing projectiles can only be downed by a lucky shot): the anterior manifestation point of the projectile and its flat trajectory mean that the projectile itself is constantly interposed between the player and the Cacodemon, so any shots directed at the Cacodemon have a fairly good chance of intercepting and destroying the ball lightning bolt.
It should be noted that a Cacodemon will always attempt to close with the player, shooting the fireballs until it is close enough to bite.
A Hell Knight is a gray-skinned towering hulk that is of prodigious weight, causing loud thuds and minor ground-shaking as it walks. Its huge muscular frames lend them tremendous physical strength, able to send a man flying twenty or so feet away with a simple left-hand slap. An in-game exhibition of its spine indicates that it has a massive skeleton as well.
The Hell Knight's head is hunched forward, supported on its thick neck and trapezius muscles, with an exposed mouth that permanently salivates. It is commonly believed that it has no eyes, ears, or nose. While the latter two have yet to be found, closer inspection shows that there are two blue-colored beady eyes in the fleshy, torn skin above its mouth. Its upper body is vaguely humanoid; the rib cage is deepened to make way for the head, and it bears only four-clawed extremities on its hands, opposable thumb included. Its leg structure resembles a goat's hind legs, much like depictions of Satan or satyrs, although the Hell Knight's terminate in feet with clawed toes instead of hooves. Likewise with the rest of the frame, the musculature is large and prominent. Much like the Imp, the Hell Knight takes on a slightly different appearance in Hell: its skin appears burned and branded, almost rock-like, and a pentagram has been seared into the flesh of its forehead. It ranks among the toughest of the non-boss enemies within the game.
The Hell Knight's deadliest attacks are close-ranged. Long-range weapons are therefore recommended to dispatch it. A fully-charged Soul Cube is the best choice of all.
The Hell Knight attacks in four ways. It can manifest and throw fireballs, perform the aforementioned slap, slash downward with its claws, or administer a vicious bite. Its tremendous endurance allows them to survive even the most powerful weapons, including a direct hit from the BFG9000 if the weapon is charged up halfway or less. The Hell Knight appears in the expansion pack, Resurrection of Evil, but its place as the strongest non-boss enemy is surpassed by the Bruiser.
In the book The Making of Doom 3, sound designer Ed Lima describes how he aimed for a "Jurassic Park/dinosaur kind of thing" for the Hell Knight's sound effects, which were created by a company called Danetracks.
The Mancubus is a gargantuan demon with an elephant-like head. A kind of "trunk" extends from under the eyes and connects to its bloated, heaving chest. Two tentacles with suckers appear near this "trunk". The suckers can be first seen in the cutscene where the player first encounters the Mancubus, when the creature is ramming its way through a grate. The designers commented that the face was inspired along the lines of Cthulhu and a shock site image of a man who took off his lower jaw with a gun shot.[ ]
The Mancubus's main method of attack is fireballs launched from twin mechanical arm-cannons. It can also attack at close-range by slamming its cannons vertically. When close enough to the player, it can inflict impressive damage with its rocket launchers. It also has the largest amount of health out of any non-boss enemy in the game. Due to its slow movement, low-velocity projectiles — such as plasma and explosives — are effective at dispatching it. A single Soul Cube attack can also kill a Mancubus with full health.
Almost every Mancubus in Doom 3 is accompanied by much smaller Cherubs.
The Revenant is an animated humanoid with transparent flesh, making it look like a walking skeleton. Its eyes glow a blue-green color, and the creature emits a dinosaur-like screech when nearby.
The Revenant attacks with homing missiles launched from shoulder-mounted rocket launchers. As the game progresses, it is revealed that the Revenant shoots its rockets by nerve reactions. It can also attack with a slash at close range.
According to the developers, the Doom 3 Revenant was supposed to be closer in design to the original Doom II monster. The introduction of the transparent skin was originally only a guide to compare the model with that of a normal human, but the modeller liked the change. It has also been stated by the modeller that the Revenant was once human but had Hell's technology implanted into it which distorted the skin and formed the demon.[
The Wraith is a hunched-over humanoid demon with long, scythe-like claws at the end of each arm. Its head is partially insect-like, with two mandibles over its mouth.
The Wraith shares certain similarities with the Imp and the Maggot, and is often considered to be related. The Wraith lacks the fireball attack of the Imp, but it has the unique ability to teleport in small jaunts. It will do this until it closes in on its opponent and will then tear him or her to pieces with its two long, scythe-like claws. Ironically, it is very easy to kill because its slow teleportation process can be easily anticipated. It is frozen for approximately a second when disappearing or spawning, but is still vulnerable to attacks. It has the same endurance as the Imp.
The Arch-Vile is a lean, pale humanoid demon with a bulbous head, long claws, and heart-like tumors on each hand. It has the ability to summon other demons from Hell to its side for aid. It attacks by shooting a wave of flame along the ground towards the player, and (as in the original Doom games) it can also momentarily set the player on fire. Because the Arch-Vile can summon other demons, it is wise to kill it before focusing on its minions. The Soul Cube is an ideal weapon to use against this demon, because the lesser demons summoned by the Arch-Vile can be used to recharge the Cube.
The Vagary is the first boss in Doom 3, and makes another appearance at one point later in the game.
While the other demons appear to be male or asexual, the Vagary is a female. The upper half of the demon is the pale torso of a woman, featuring six spider-like eyes, bony arms, breasts lacking nipples, and a bald head. The bottom half is that of a black spider with a large, transparent abdomen. A large human or Mancubus fetus appears to be gestating inside the abdomen. She is assumed to be the mother of the spider-like demons, the Trites and Ticks. She is considered one of the most disturbing demons in the game, due to her appearance. When she is first seen, her lair is a large room with web strewn everywhere. Along the ceiling, hanging human victims entangled in the web can be seen.
Her methods of attack are claw slashes at mêlée range and telekinesis, which is used to hurl objects at range. The lair of each Vagary is littered with multiple large spiked rocks or rigid egg sacs, which are the objects most often thrown by the Vagary.
The Guardian of Hell
The Guardian of Hell, or simply known as Guardian, is the second boss in Doom 3. It is seen exclusively when the player reaches the end of the Hell level. However, in the expansion pack Doom 3: Resurrection of Evil, the head of the Guardian is engraved on some stone tablets.
The Guardian looks vaguely like a Tyrannosaurus rex (the designers commented that the Guardian's appearance was driven by the idea of a pre-human Hell, with the Guardian a demonic opposite of dinosaurs [), but with larger and more muscular arms ending in large round fists that appear to contain cracks full of ]lava, muscular legs with hooves, a hunched upper body, a very long tail ending in a ball covered in cracks full of lava, an armored back with traces of lava, and a head that has stereotypical demonic horns. It is blind (due to age, according to the designers[), and what remains of its eyes are shallow pits. It summons much smaller (and possibly cybernetic) creatures dubbed Seekers to "see" for it and locate its targets. Once its Seekers locate the player, the Guardian charges towards the player with crushing force. The best way to deal with the Seekers is to use the rocket launcher, due to its high splash damage. Its refuge is a large area of Hell that is filled with large pillars of rock and large slabs of dead demon flesh are strewn on a few of them. ]
Its primary attacks consist of punching with its large fists and pounding the ground, which emits spheres of energy that damage its target. It has a weak point: if the Guardian's seekers are destroyed, a glowing orb of energy appears out of an opening in the Guardian's back. Severely damaging this orb will kill the Guardian. After killing the beast, the Soul Cube is released and its body does not dissolve (unlike some other demons).
Sabaoth, or Sarge, is the third boss in Doom 3. Sabaoth is the demonized and mechanized form of Sergeant Kelly. His torso, head, and arms are mounted on a tank-like base. What remains of his body has been horribly mangled and devastated, merging with the mechanical parts grafted onto him, much like the Strogg in Quake II and Quake IV.
Sabaoth attacks with the BFG stolen from Jack Campbell, as well as the small mechanical claw mounted on his right arm. If the Soul Cube is "charged", it is very easy to kill him: one attack with the Soul Cube plus five direct rockets on the torso will kill him (on any difficulty level). The player can also run at Sabaoth and use the chainsaw to kill him in seconds, but the player can take an extreme amount of damage and it is not the best strategy to use when low on health.
The Cyberdemon is the final boss of Doom 3, and cannot be hurt with conventional firepower by a solo player; instead, the player has to utilize the most powerful weapon in Doom 3, the Soul Cube, to kill him. However, when playing in a cooperative mode (Xbox Live), the Cyberdemon can be killed with normal weapons.
The Cyberdemon is by far the tallest monster in the game, towering several meters over the player, and is a gruesome mixture of both demonic and cybernetic parts. His main attack is with the rocket launcher mounted on his right arm, opposite from its location in the classic "Doom" games. He can also eliminate opponents by stepping on them, ending the player's life instantly.
Many players complained about the fact that the Cyberdemon is no longer vulnerable to the other weapons, and thus, a mod was released weeks after the release of Doom 3 that made the new Cyberdemon vulnerable to conventional weapons. Future source ports for Doom 3 may have settings allowing the Cyberdemon to be vulnerable to conventional weapons. Some players have altered the boss themselves, modifying the monster_boss_cyberdemon.def of pak000.pk4 by changing the "finalBoss" value to "0".
The Forgotten One's form is an echo of the original Lost Soul's shape in the previous Doom games. It is a flying skull with two demon horns, floats with a stream of flame behind it, but lacks eyes. Like the Doom 3 incarnation of the Lost Soul, which is absent in the expansion campaign, the Forgotten One's only attacks are charging towards its enemy and biting. However, it is not capable of inflicting as much damage, is a larger target, and is easily dispatched by the Grabber.
The Vulgar resembles an Imp although there are some bodily differences. The Vulgar have only two eyes that have an orange glow. It is slightly shorter and has a monkey-like frame instead of human. Due to this, it moves on all four legs but will stand up on its hind legs when attacking. Unlike the Imp, it supports a long tail, its bellies have small insect-like limbs attached, and its lower jaw is designed like an insect's mouth parts. It also differs from the Imp because its fireballs are cyan as opposed to the Imp's orange fireball.
Its fireball attack is comparable to the Hell Knight's version, though it is significantly weaker — even weaker than the Imp's fireball. The other attacks consist of leaps and claw slashing. It has a mechanical-like growl that it emits in each attack and is also capable of crawling on walls and other surfaces. Unlike other monsters, its spawning cloud is cyan rather than orange.
Vulgars seemingly replace the Imp in the Doom 3 expansion pack, as once the Vulgar appears for the first times, Imps are rarely seen. Vulgars also appear just as frequently as Imps had in the original Doom 3, but hardly, if ever, lurk in secret doors in the wall or in vents.
The aptly named Bruiser has a large muscular body in the vein of a Hell Knight and identical mechanical features of a Mancubus, although both creatures' robotic parts look different. It is also slightly taller than the Hell Knight. Its feet feature robotic hooves and both arms are giant rocket launchers. The head has two demon horns on the far back, facing outward, and the front has two yellow eyes with no pupils. Above the eyes are two yellow rings. The mouth is actually a large TV-screen that connects to the head with a fleshy tube. On the screen is a close up of a (presumed) angry human mouth, showing only gums and teeth. The TV-screen also displays an eyeball upon sighting an enemy. The mouth sometimes opens and closes as the beast moves. Its back has what appears to be a visible, robotic spine. Despite its large frame, the Bruiser can easily maneuver in and out of doorways like the player can, making the Bruiser very hard to effectively run from.
Seen early in Doom 3's development, the Bruiser's unique TV-like mouth was intended to be another way of surprising the player. The player would walk up to what appeared to be a typical computer terminal, and the terminal would change and the Bruiser would reveal its entire self. [ This, however, does not happen in any point in the game. ]
The Bruiser attacks by rapidly firing its cannons, which will quickly kill almost any opponent. Its endurance is even higher than that of the Hell Knight or the Mancubus. The best ways to kill it are to either shoot the TV screen with the strongest weapons available, or to use the berserk power from the Artifact and attack with the fists. Two double-barreled shotgun blasts or one punch will kill it whilst in berserk mode.
The Hell Hunters are creatures resembling Hell Knights sent from Hell by Dr. Betruger to track down The Artifact and the human who wields it. There are three different Hell Hunters: the Helltime Hunter (with the ability to slow down time), the Berserker Hunter (ability to deal significant damage with mêlée attacks), and the Invulnerability Hunter (ability to become invulnerable by feeding on the generators in the room in which it is battled). Each is fought separately throughout the game. When one is killed, the Artifact becomes stronger, appearing as if the Hell Hunter's soul or life essence is absorbed into the Artifact.
The Maledict looks like a dragon with a large set of wings, two legs with clawed feet, a long tail, and a head shaped like a demon skull. It has empty eye sockets (and is thus possibly blind or sees via supernatural powers) and emits a loud, piercing scream. It is not known whether Betruger is a part of the monster or if he is controlling it. Either way, he does not seem to mind, as he apparently sees his new form as preferential to staying human (referring to everyone as "Mortals" in Resurrection), most probably meaning that he has completely let his almost invulnerable state power his ego. Resurrection's ending cinematic shows that the demon is very large compared to humans, able to swallow them whole.
The Maledict does not seem to attack the player directly, but instead conjures other means to attack the player. The Maledict can be seen summoning Forgotten Ones to attack its foe. Whether or not it can summon other enemies into the fray is not yet identified. However, since Betruger can be heard cackling while enemies are being summoned during the course of the game, it is safe to say the Maledict does have this ability. The Maledict can also call down a flurry of flaming rocks to attack its foe and can also create a fire wall to attack the player just as the Arch-Vile does.