- "My Guardian will destroy you!"
- ― Betruger [src]
The Guardian of Hell, or simply known as the Guardian, is the second boss in Doom 3. It is seen exclusively when the player reaches the end of the Hell level. This crocodilian-like demon stands more than 15 feet tall, just a little over 2.5 times taller than a human soldier. It guards the Soul Cube and the player must defeat it to obtain the Cube.
The Guardian looks vaguely like a crocodilian, but with a taller and broader jaw, and larger and more muscular arms ending in large round fists shaped like Morning Stars that appear to contain cracks full of lava, muscular legs with hooves, a hunched upper body, a very long tail that ends with a spiked mace similarly to its arms, an armored back with traces of lava, and a head that has stereotypical demonic horns. The designers commented in the Making of Doom 3 book that the Guardian was created with the idea of a pre-human hell during the prehistoric age, and it was something that dinosaurs feared and perhaps caused their extinction.
Its refuge is a large area of Hell that is filled with large pillars of rock and slabs of demon flesh can be seen strewn on some of them.
Its primary attacks consist of punching with its large fists and pounding the ground, which emits large spheres of energy that burst from the Guardian in all 8 directions. It can also charge at you.
The Guardian's tough hide renders it invulnerable to all forms of weapons fire. The only way to harm and kill this goliath is to take out its Seekers. When all the Seekers are dead, the Guardian stops and forms a blue sphere above its head, which generates more Seekers. This blue sphere reveals a glowing energy orb in the Guardian's back; this orb is the beast's only weakness. However, this weakness will only show itself for 5 seconds.
- "Destroy the Seekers, and the Guardian becomes vulnerable."
- ― The Soul Cube [src]
The Guardian of Hell is blind due to its age; what remains of its eyes are shallow pits. In order to 'see', It summons smaller creatures called Seekers, as spotters. Only three can be active at a time and search for your location. When one of the seekers spot you, it directs the Guardian to charge at your location.
Killing the three Seekers forces the Guardian to generate more, revealing its vulnerable spot: a glowing orb of energy in an opening of the Guardian's back. Shooting this orb is the only way to kill the Guardian. As you fight the Guardian, the Soul Cube will inform you of this weakness.
The Guardian is relatively easy to kill if you can manage to avoid the energy spheres. Kill the seekers with the plasma gun or the rocket launcher, and when the glowing energy orb appears, unload your chaingun into it. This should kill the beast in 4 rounds (3 if you aim well). It is also possible (although difficult) to kill the monster using 2 charged BFG shots. For those seeking a quick end, a single, well-placed shot from the BFG can destroy all of the Seekers at once, rendering the Guardian vulnerable much quicker.
After killing the beast, the Soul Cube is released.
Unlike most other demons, the Guardian's body does not dissolve.
In Resurrection of Evil the head of the Guardian is engraved on some stone tablets. This could mean that either the Guardian left Hell to assist in the invasion, some of Mars' civilization saw it in Hell, there may be more than one Guardian, or it was simply aesthetically pleasing to the game's designers.
He appears as the final enemy guarding the captured teleportation unit located deep inside Hell. This Guardian uses similar attacks as the regular version, but is not blind and so dosen't need Seekers. Instead he lobs a series of mortar-like energy balls from his back. Moreso, he can be harmed by regular weapons fire, and does not need to be hit in a weakspot. However, he has significantly more health than the regular version, being able to withstand about 30 rockets or 3 or 4 fully charged shots from the BFG 9000 before falling (which would make his health on par with that of the Cyberdemon and Maledict, the final bosses of the game's other campaigns). Additionally, hitscan projectile hits on him only seem to register during and immediately after one of his attacks.
A prominent promotional artwork image for the Doom 3 BFG Edition features the Guardian of Hell looming in the background while the Bravo team survivor is engaged in a combat pose in the foreground.
It could be speculated this may be a younger Guardian, as it hasn't lost its sight with age and is tougher than its elder variant.