I can't believe I didn't mention this earlier.
Drinniol, from
Marathon 1.
Big, slow-moving blue-skinned and blue-blooded bullet sinks. Used to decent effect on the level
The Rose, where they served as an effective way to overcome certain engine limitations (I believe only about a baker's dozen creatures could be "awake" at a given time in the original engine, so you'd need a relatively small number of creatures in a given encounter if you wanted them all to be active and able to occupy your full attention), while still allowing you to save (one or two of) the civilians in the entry rooms. Just keep the Hulks' attention while focusing your own efforts on actually killing the faster and more numerous fighters, and don't grenade your own civilians or defense drones. (Easier said than done, of course. Also, any and all strategies are made useless on Marathon 1's Aleph One port, where Leela gives you the "failure" message no matter what the outcome of your mission, making her seem like a bit of a bitch).
Used to poor effect on the level
Blaspheme Quarantine, where their bullet sink properties only serve to make the level slightly more irritating and time-consuming.
(I do kinda enjoy punching them to death, though. There's an actual feeling of having overcome a slight challenge there.)
Never used again in the canonical series, occasionally pop up in fan scenarios. Possibly notably, turned from time-consuming bullet sinks into vicious and unduly difficult enemies in Rubicon and Rubicon X, where they throw a constant stream of ridiculously fast-moving bouncing grenades at you instead of bringing their fists to a rocket fight like honorable aliens.
Craig Mullins made a digital painting attempting to capture the feeling of almost-pathos I and other players felt upon watching the Drinniol death animation. They make this sound, sort of a moan/death rattle, and in-story you learn that they're just poor abused slaves, not monsters at all--which really goes miles to explain why they aren't given real weapons, too, another way Rubicon's grenade-spewing blue-skinned abominations seem out of place.