Source: dccomics.com
4. Mongul
Look, when you’re a big strong murderous dude, and you need something to keep you entertained, you fall into some pretty strange life paths.
One of those life paths was commandeering a big mechanical planet called Warworld and abducting various badasses so that they could fight to the gladiatorial death in your arena while thousands watched and cheered. That was the path Mongul took. And said life path got him punched right in the kisser by Superman.
After this, he fled to a tiny planet, and got impressed into service by Cyborg Superman, who sent him to earth under the premise of making him a new Warworld. Mongul destroyed Coast City, killing everyone in it and building it into the horrific Engine City. After this plan also got him face-punched by Superman, Mongul decided to go fight the Green Lantern for a while.
Eventually, he was taken to hell by Neron, who offered to buy his soul for a power upgrade. Mongul tried to fight Neron, and Neron promptly, and without effort, killed him.
