Conceivably the most formidable foe in the original Doom video game, the Cyberdemon is a huge, minotaur-like beast with two large horns on its head, a rocket launcher for an arm, and various cybernetic components making up parts of its body.
The Doom II PC manual describes this monstrosity as "A missile-launching skyscraper with goat legs. 'Nuff said." While the original Doom PC manual didn't mention the Cyberdemon - presumably to have its first encounter be a surprise for players - the various console versions of Doom describe the Cyberdemon as: "Half unfeeling machine, half raging horned devil. This walking nightmare has a rocket launcher for an arm and will definitely reach out and touch you. Make sure you're loaded for bear before you take on this guy."
The Cyberdemon serves as the final boss and most powerful monster of Doom 3. It's even bigger than before, at least three times taller than the player, and still shoot missiles as its primary attack. Several changes have been brought to its appearance however. The Cyberdemon is now considerably more cybernetic than before, with both legs mechanical instead of just one, its head is a massive mess of metal plating with some of it even going down its back and terminating in a long tail, and the rocket launcher has switched from its right arm to its left one. Clearly, it more than matches up to its old Doom II description.
Powers & Abilities
When attacking, the Cyberdemon fires a barrage of three rockets, the explosions of which can do significant splash damage. The Cyberdemon itself is immune to all forms of splash damage, and can only be injured by direct hits from weapons. Killing a Cyberdemon takes a massive amount of ammunition. Even the legendary BFG-9000 takes three to four direct hits to kill it. Also, while most monsters in Doom can flinch when being attacked, the Cyberdemon is unaffected by this and will keep attacking no matter what until it is dead.
Originally, the Cyberdemon didn't have a true melee attack for close quarters combat, but later versions of Doom gave it the ability to violently stomp on the player, an instant kill attack.
The Doom 3 version of the Cyberdemon was even tougher, as he was entirely immune to all forms of conventional weaponry. Only the demonic Soul Cube, the game's most powerful weapon, could kill it. Even then, it took four hits from the Soul Cube to kill the beast.