Spiderdemon

The Spider Mastermind (also called the Spiderdemon) is a die-hard creature (with 3000 hit points) and is the boss of Episode III (Inferno) of Doom and Episode IV (Thy Flesh Consumed) of Ultimate Doom. Her weapon is a big machine gun that has the sound of the shotgun but with a spread similar to the player's chaingun. When a Spider Mastermind begins firing, she will not stop until her target moves out of her view or dies, if she is stunned (causing her to move) or if she is killed. Similar behavior can be observed with the Chaingunner and Arachnotron.

The Doom II game booklet says:
 * The Spider Mastermind: You guess the Arachnotrons had to come from somewhere. Hi, mom. She doesn't have a plasma gun, so thank heaven for small favors. Instead, she has a super-chaingun. Crap.

The Spider Mastermind is not mentioned in the Doom game booklet, presumably to avoid a spoiler. Perhaps as a result, the game booklet for the Depths of Doom Trilogy erroneously states that she appears in Doom II only.