A big floating monster that appears in Doom, Doom II and Doom 3. It's red, with horns and a huge mouth. It's also one-eyed. It moves slowly and its only attack is throwing a white fireball at you. They aren't very tough, but if you don't move they'll toast ya.
In Doom 3 they look different, smaller, and their attack is more powerful.
A horrible and terrifying enemy seen in every Doom computer game yet, the cacodemon was not seen originally until approximately halfway through the first game. The cacodemons were originally red floating cycloptic spheres, but got an extreme makeover for Doom 3. Fast, very powerful, hard to kill, along with the fact that they often attack in swarms or close quarters, or in the shade where you can't see them, are the main reasons why the cacodemons remain a favorite enemy of many fans to this day... and what made them the worst enemies to face other than bosses.
I just got blasted in the face by a lightning ball (their only attack) from that cacodemon.