The Cyberdemon did not make an appearance in the expansion pack Resurrection of Evil, so the one that was killed at the end of Doom 3 was presumably the only one.
The Cyberdemon is also the only monster from the original games to be a boss.
It stands roughly 20 feet tall, more than 3 times as tall as a human soldier. While the Cyberdemon overall retains its appearance as a minotaur-like giant, there are some differences of this new incarnation of the monster compared to its classic counterpart. This incarnation has a long tail, extending from the machinery on its back, and both legs are mechanical - as opposed to its original version, whose only mechanical leg was the right one. Another noticeable difference is that its rocket launcher is now located on the right arm instead of the left one.
Like its original counterpart, the Cyberdemon attacks by firing a salvo of 3 consecutive rockets from its arm-mounted rocket launcher. Unlike the original version, it now has a melee attack as well: the monster can stomp on the player, killing them instantly.
Unlike its original counterpart, it cannot be hurt with conventional firepower; instead, the player has to utilize the most powerful weapon in Doom 3, the Soul Cube, to kill it. The Soul Cube states that only it can kill "Hell's mightiest warrior" presumably referring to the Cyberdemon. It takes 4 shots from the Soul Cube to kill the Cyberdemon. Fortunately, there are plenty of lesser demons on the level that can be killed to charge the Soul Cube.
The basic strategy for taking down the Cyberdemon is to always be on the move. Do not stay for too long in one place for any reason or the Cyberdemon will nail the player with its rockets. The player's stamina does not decrease near the Hell Hole, so take advantage of this and use sprint constantly. The Cyberdemon's rockets are fast, powerful, and long ranged, but fortunately the rocky spires around the Hell Hole prevent the Cyberdemon from getting a clear shot at the player. However, do not get too close to the ledges as the blasts from the rockets can knock the player into the Hell Hole to their death. Also, do not even think about going near the Cyberdemon: its melee stomp will crush the player instantly.
Throughout the battle, the player will be constantly attacked by Imps and Maggots, which will either teleport in or come crawling out of the Hell Hole. The player can kill these demons as fast as possible to get the player's Soul Cube operational. Use the Rocket Launcher or the BFG to one-shot these demonic lackeys. No need to worry too much about picking up any health units on the ground, since the Soul Cube will heal the player. And, remember, always stay on the ground and keep out of the Cyberdemon's line of sight until the Cube is ready.
Once the Cube is powered up, turn around and face the Cyberdemon itself. As soon as the Cube has been launched, get out of the Cyberdemon's line of sight and start running again. Be sure the player's targeting reticle is focused on the Cyberdemon before launching the Cube. If there's an Imp or a Maggot nearby, the Cube may end up going for it instead of the Cyberdemon, thus wasting the player's shot.
After four hits with the Soul Cube, depending on the difficulty, the Cyberdemon will go down and you win the game.
- The Cyberdemon can be found in the game files of the Doom 3 expansion Resurrection of Evil, but when it is spawned (for example by using a cheat code), the Cyberdemon appears to be vulnerable to regular weapon fire, requiring lots of rockets, BFG blasts, or Plasma Gun cells to the head in order to fall.
- Logically, the Super Shotgun may work against the Cyberdemon, but it is not recommended due to the instant-death stomp attack the Cyberdemon possesses.
- The Cyberdemon is referred to as "Hell's Mightiest Warrior" by the Soul Cube, although the Maledict has more hit points. This is likely because, unlike the Cyberdemon, the Maledict is vulnerable to conventional weapons.
- In the final cutscene of Doom 3, the Soul Cube cuts off one of the Cyberdemon's legs, the one opposite the rocket launcher. This may be a callback to Classic Doom games, where the Cyberdemon had one robotic arm and one robotic leg. However, the arm and the leg are switched from the original version (the cut-off leg is on the left instead of the right). Since the Soul Cube killed the Cyberdemon immediately after its leg becomes amputated, there was never a chance for its leg to be replaced by machinery. Both of the Cyberdemon's legs are robotic this time, instead of just one.
- If spawned in some places, the Cyberdemon will become stuck because it will have its body trapped in the ceiling. This is rather annoying, as it is very difficult to walk past the Cyberdemon without noclipping through it.
- If noclip is used to get close and you punch the Cyberdemon, blood will come out of the robotic parts.
- This incarnation of the Cyberdemon bears a resemblance to the Balrog from Peter Jackson's film adaptations of The Lord of the Rings, who actually also partly resembles the Maledict.