The Scourge have existed since the dawn of humanity, having preyed on Australopithecus and its descendants. They are nearly always unseen: nothing more than a strange presence that inhabits the mind in a subconscious level. While they usually behave as parasites - both stimulating and feeding off the host's negative emotions - they are also able to overtake their victims' minds and even physically possess them and transform them into Scourge if they wish.