The Mercurian Renegade
Nemesis: Martian Manhunter
Other Major Foes: None
Appearances: One comic story.
Powers: Super-strength, invulnerability, a disintegrator gun, and a small spaceship.
Bio: The Mercurian Renegade landed his one-man ship in France, and decided Earth was as good as any planet to conquer. He was aided by the super-powers he developed in Earth's atmosphere, but the similarly empowered Martian Manhunter showed up to send him packing back to the stars.
Lose: The Saturnian Criminal (1-?); The Invaders from the Space Warp (4-7)
Nemesis: Green Lantern
Other Major Foes: The JLA.
Appearances: 60+ comics and an episode of Justice League Unlimited
Powers: The Sonic Sceptre allows Sonar to lift and carry objects (including himself,) project a force field, absorb & weaponize sonic emissions, as well as create illusions.
Bio: Bito Wladon was born to deaf parents in the minuscule European nation of Modora. A backwards, superstitious people, the Modorans shunned the deaf, inspiring the unimpaired Wladon to pursue inventions related to sound. Bound to prove both his self-worth and the greatness of his country, Wladon became "The Sultan of Super-Sonic Sound," using specialized weaponry in pursuit of crime and international conflict.
Sonar is one of those harmless Silver Age megalomaniacs that DC has of course tried to turn into Magneto/Dr. Doom or replace with a more gnarly successor, but it won't take. He dresses like Napoleon and plays with a tuning fork gun. That'd how he rolls. He's fought virtually every earthbound Green Lantern except maybe Kyle Rayner (who tangled with two short-lived revision attempts instead,) and that deserves respect. The Mercurian is one of the cooler looking alien bad guys to fistfight the Alien Atlas, which is nothing to sneeze at, either. This could go either way, depending on circumstances, but I lean toward Sonar's versatility. Plus, I keep forgetting that the Mercurian didn't have the air-bubble-trap-rifle-thingee in his one story, which would have been a more formidable gimmick than a garden variety ray gun. If the Renegade ever comes back, I hope he steals that dealy from Vulture. I'd like the poor alien to win at least one of these matches someday.