An ancient race of evil creatures, older than life itself, and older than the demons who feed off life. While the demons seek to corrupt the mortal souls of the deceased into more demons, these guys simply seek to wipe out the phenomenon of life as a whole. They hate the demons and have been at war since forever. In fact they are almost extinct from that war and the few remaining survivors spend most of their time hiding in the deeper levels of the Abyss or in the Void between planes.
These guys come in a wide variety of horrifying shapes and sizes. One special example is a gargantuan many-winged spellcasting monstrocity that shoots disentegration rays from his manifold of eyes, and hunts entire worlds. He is so terrible that the universe only allows one to exist at any one time. He can be destroyed but the universe will inevitably churn up another example.
I think these guys are part of the 3.5 material. They were certainly part of an addition where monsters had a spell list. I remember the big guy had dimension door.
I also remember the race's name started with either a 'p' or a 'q' and had an apostrophe in the middle.
Do they sound familiar to anyone?