An alien parasite once latched on to another moutainous alien; The combined being took the name Overmaster and journeyed through space, interfering with sentient worlds. When this being arrived on Earth, it saw a planet full of super heroes and recognised a new way to test the populace. Overmaster recruited 6 humans and formed the Cadre. This group challenged the Justice League to battle with the fate of humanity at stake. The JLA prevailed. Overmaster returned for man's "Judgement Day" and again faced the League.
It is not known how long he has wandered the cosmos before arriving at Earth, but along the way he accumulated many alien prisoners, many of whom are the last of their race, including Yazz.