Bio-suit zombie

The bio-suit zombie, also known as a hazmat zombie, is a monster first included in Doom 3: Resurrection of Evil, and occurring again in The Lost Mission. The bio-suit zombie, normally found in toxic areas where there is no oxygen, wears a yellow hazmat suit. They behave much like normal zombies, slashing at nearby players. When killed, they drop valuable air tanks, which help the player stay alive much longer in toxic or low-pressure areas. This enemy is rare, occurring in only one level of each expansion.

Development
Screenshots released early in the development of Resurrection of Evil depict the bio-suit zombie as wearing a dark grey hazmat suit that has a red band just below each elbow. This design was originally used for certain NPCs in the base campaign, such as Dr. Michaels and the unknown person who emerges from the Delta 4 teleporter only to be killed immediately by Hell knights. It is unclear if this earlier version of the monster was ever intended to be the final version of the monster, or if the version was merely a stand-in until a later design could be finalized.