Parallax is a demonic parasitic entity dating back to the dawn of time. This parasite was the sentient embodiment of fear, traveling from world to world and causing entire civilizations to destroy themselves out of paranoia. The Guardians of the Universe imprisoned Parallax within the Central Power Battery on Oa using fear's opposite energy, willpower. Parallax had lain dormant for billions of years, its true nature hidden by the Guardians to prevent anyone from trying to free it. Being yellow in color, Parallax eventually came to be referred to as simply "the yellow impurity."