Mongul the Elder
Mongul is an alien world-conqueror and the leader of Warworld. His brutal and merciless nature make him an enemy to Superman and a threat to the larger universe. His specialty is using the Black Mercy plants to incapacitate his opponents.
Despero is an intergalactic conqueror and enemy to the Justice League of America. He has been a member of the Injustice League, Secret Society of Super-Villains and the Time Stealers. The ruthless tyrant ruler of planet Kalanor, he possesses incredible mental powers in addition to his great strength and intellect.
Steppenwolf lead an army against Earth 2 in the name of Darkseid during the Apokolips War, where he kidnapped the daughter of Wonder Woman and began to train her as his bodyguard, naming her the Fury. Steppenwolf later killed Wonder Woman and Superman during their last ditch attack against him. He was, however, defeated after Batman sacrificed his life to send all of Steppenwolf's Parademons back through boom tubes.
Steppenwolf then spent the next five years in hiding trying to escape the World Army with the help of his remaining forces and Fury. Steppenwolf later took control of the small country of Dherain after killing their king and set up plans to conquer the world.
The being known as Starro the Conqueror was once a little boy named Cobi who lived peacefully along with his people (specifically his brother Andrez) on the "unremarkable" planet Hatorei. The Hatorei people lived simple lives and they had few semblances of a developed world but in one respect they were unsurpassed. Once a day the planets inhabitants would congregate in a species-wide telepathic link and open up to each other which made their society the pinnacle of ethics and cultural stability.
Now Starro the Conqueror, he used his control of the Star Conqueror species to begin a series of war of conquests. While he would enslave most foes with Star Conqueror starfish, he would grant some particularly useful opponents larger starfish to wear upon their backs and a place at the head of his armies under him, allowing them free will so long as they turned their talents towards his conquests. As his empire's expansion continued, he was able to draw power from everyone so controlled. Between his mind-controlling staroos, ever-growing strength and his still independently thinking elite, his forces were unstoppable, leading him to gain control of nine galaxies.