Nemesis: Martian Manhunter
Other Major Foes: Justice League of America
Appearances: 2 original comics
Powers: Superior strength and reflexes rivaling the Martian Manhunter's. Shape-shifting, super-hearing, flight, invisibility and limited invulnerability. Likely more, as common amongst Martians.
Commander Blanx led a Pale Martian army to successfully seize control of his home planet's greatest energy source, the Blue Flame. The opposing army of Desert Dwellers had followed science leader J'onn J'onzz, whom Blanx encountered in single combat, but defeated with the help of others. Blanx exiled J'onzz, however when the Martian Manhunter turned up on Earth, the Commander followed with a troop in an assassination bid. These "invaders" caused a national hysteria, prompting the largest assembly of 1950s era heroes ever seen. At one point, Blanx traded blows with Superman, but his group was ultimately defeated by the heroes who would eventually form the Justice League of America.
Commander Blanx returned to Mars, and about a decade later, brokered a deal with unnamed aliens to sell the planet. The catch was that Blanx had to wipe out all other life on the world, which he did by releasing the Blue Flame of Mars. The Justice League routed Blanx's forces and the Martian Manhunter engaged the Commander in mortal combat for his genocidal conniving.
Win: Vandal Savage (11-6,) Kanto (10-7,) Professor Amos Fortune (7-2,) The Marshal (9-5,) Mr. V (4-3,) B'rett (11-2,) B'enn B'urnzz (7-1,) The Devil Men of Pluto (8-2,) Captain Destiny
Lose: Despero (7-3,) Malefic (5-2)
Nemesis: Iron Munro
Other Major Foes: Wonder Woman, Damage, All-Star Squadron
Appearances: Less than fifty comics total.
Powers: Superhuman strength, relative invulnerability, eye lasers, and flight.
A Nazi deformed by acid thrown in his face by a concentration camp prisoner was experimented upon by Aryan scientists. The results made him both greater and less than human. With his new superpowers and a suit of armor, Baron Blitzkrieg first battled Wonder Woman, then the larger All-Star Squadron. The Baron not only survived the collapse of the Third Reich, but remained active in international criminal circles over half a century later. The Baron was part of Vandal Savage's project to create Damage, whom he fought several times (often joined by his most persistent foil, Iron Munro.) The Baron was finally killed by Superboy-Prime during Infinite Crisis.
Idol Speculation: Commander Blanx can last a few panels against Superman and a few pages against the Martian Manhunter, but he's really dependent on his Pole Dwellers to be any kind of threat at the stakes he plays at. Baron Blitzkrieg could go a few rounds with Wonder Woman or several lesser JSA members at once, but it always comes down to nameless minions getting slapped around in a bunker somewhere while the Baron escapes to plot another day. I like the match-up of powers, since Blanx didn't ever get to display a full complement of Martian abilities, and the Baron was basically the early lower-powered Siegel & Shuster Superman working for the Axis. Blitzkrieg has had a lot more opportunity to strut his stuff, but his greatest accomplishments include killing the Red Bee and the infant son of Iron Munro and Phantom Lady. Commander Blanx destroyed Mars and inspired the secret formation of the JLA. Blitzkrieg was a Super-Nazi, but Blanx was Space Hitler, wiping all but a few hundred surviving denizens of the Red Planet. Since I've never believed in a Martian overlord falling to his death from a staircase while being squashed by a plaster globe, I favor Blanx in the event that anyone ever bothered to use him again.