Though initially introduced as villains in the 30th century of the Legion of Super-Heroes, they appeared in the 20th century in the company-wide crossover Invasion!, in which they were the primary world behind the Alien Alliance that attacked Earth. Their primary motivation for this was their concern at the genetic potential of humanity, as evidenced by the large number of super-powered beings on the Earth of the DC Universe, also known as the metagene. When the Invasion started to crumble, one Dominator created a 'gene-bomb' and detonated it in Earth's atmosphere that would affect many heroes and villains that possess the metagene.
After the Invasion, a nameless Dominator played a significant role in the comic book one shot Blasters. This comic features heroes created by Dominator testing; they had wished to examine just how humans tended to gain superpowers. This testing involved running humans through a murderous obstacle course on the partly correct theory that the stress would active their 'meta-genes' and cause superpowers. The 'Blasters', which included former JLA mascot Snapper Carr, are the ones who did gain powers.
In events chronicled in Legion Annual v4 #2, Valor discovered plans for a second invasion of Earth, and thousands of humans held in genetic experimentation tanks