ALIENS AND SO FORTH ROUND-UP 050

All these fictional aliens and we don't even get one other inhabited planet in our solar system.

Moon-Men:

These Moon-Men are encountered by Phantasmo (seen here in his less-nude human identity) and his pal Whizzer McGee during an impromptu trip to the Moon. They live deep beneath the satellite's surface and appear to have a mining-based culture that is pretty hostile to outsiders, and that is all we know. While I must commend the "Phantasmo" team for not automatically making every alien race fluent English speakers or gifted telepaths, it does make for a more limited mode of storytelling. "Why are the Moon-Men mad at us, Phantasmo?" "No idea." (The Funnies 060, 1941)

Inhabitants of Ru:

These very humanoid Martians are encountered by Flint Baker and his convict crew upon making the historic first second rocket voyage to Mars. They very specifically inhabit Ru, which is either the name of their country or the entire Light Side of Mars, and are a peaceful society in that sci-fi way that means that they are completely unable to deal with threats. Flint is thus required to save them from both the Earthman Sarko (late of the actual first manned mission to Mars) and then the diabolical Creature and his monster. (Planet Comics 001, 1940)

One-Eyed Monster Men of Mars: 

And speaking of Sarko, his plan to conquer Ru revolves around the One-Eyed Monster Men who inhabit the (non-existent) Dark Side of Mars. Though they are intensely fun-looking creatures, the One-Eyed Monster Men don't get a lot of character development in the course of the story due to being mere foot soldiers and also possibly mind controlled.  (Planet Comics 001, 1940)

Martians:

As the "Spurt Hammond, Planet Flyer" series is at least initially set in the year 40 000 CE, there is a strong possibility that both the Martian and Venusian peoples pictured above are descended from some long-ago human colonists. Heck, that might just be the best backstory to explain a planet of warlike Martians or of peaceful Venusians who name their kids things like "Amoura:" because they have built their societies around the cultural assumptions and legends that tie into their planets. (Planet Comics 002, 1940)

Despite the fact that Spurt Hammond managed to resolve the conflict between Prince Khangiz of Mars and Queen Amoura, Venus was clearly subject to some sort of political upheaval because just four issues later the planet is ruled by Queen Veloptan. Perhaps Amoura was determined to be just a bit to on-the-nose, even for Venus. (Planet Comics 006, 1940)

Venus is another one of those conflict-averse pacifist societies, and just two issues later they are turning to Spurt Hammond once more. This time the entire planet is swiftly becoming uninhabitable and the population are forced to become refugees, prompting this array of Plutonian, Saturnian and Jovian rulers doing their best impressions of WWII 20th Century most world leaders throughout modern history. And as a bonus: a new Martian leader named Kaga! (Planet Comics 008, 1940)