Despite the wide number of different aliens that we have covered thusfar, there are so many aliens left to go!

Dragon-Men:

These Dragon-Men of the planet Ligra, or at least their leader King Jago, have ambitions to rule the entirety of their world, and so ambush and capture Electro and Professor Zog in order to use them as war machines against the hated Lion-Men. (Marvel Mystery Comics v1 008, 1940)

Though Professor Zog is a firm believer in freedom over tyranny and so rejects Jago’s demands out of hand, one of the endearing things about him is the fact that he is just a regular frail human. He might have the mighty power of Electro at his fingertips, but if you strap him into a weird alien torture device, he’s going to crack eventually. Electro is officially drafted into the Dragon-Men’s war. (Marvel Mystery Comics v1 009, 1940)

Lion-Men:

The other inhabitants of Ligra and subjects of this aggression are the Lion-Men, who are easily identifiable as the Good Guys because they are ruled by a beautiful Earth woman named Nara who is the daughter of one of those comic book scientists who make sure to include their spouse and infant children in all of their most dangerous experiments, up to and including flying an experimental “stratosphere-plane” to an unknown exoplanet.

Electro kicks the hell out of the Lion-Men until Professor Zog manages to pull a fast on and reassert control over his own destiny/robot. The Dragon-Men are defeated and most importantly King Jago bites the big one, ending the threat of his expansionism for good. (Marvel Mystery Comics v1 009, 1940)

Mermen:

These Mermen work for the villainous Murdo and are fairly unremarkable save for the fact that they live in a lake in India, which is hardly the first place you think of when you think of merfolk. (Prize Comics 005, 1940)

Venus Amazons:

Flint Baker is hanging around with his pal at the space gas station one day when the body of a Venus Amazon floats up to them. Investigating, he discovers the entire Amazon population hanging in space in a fleet of primitive spacecraft that are not rated for the altitude that they are at, and the only reason everyone doesn’t die is that Flint tows them all back to the surface.

So why were they up there in the first place? Turns out that they were attacked by a group called the Metal Men, who may or may not have originally come from Venus but who were far more prepared for war than the Amazons, who seem not to have developed weaponry beyond the spear and the double-headed battleaxe.

Flint solves this problem by arming the Amazon forces from the frankly concerningly-large stockpile of ray guns that he keeps on his ship and the Metal Men are soon routed.

Though the Metal Men are spoken of as though they are some sort of robots, they certainly look like guys in metal armour to me. Despite this, when Flint and the Amazon Queen Futura go looking for a central control station from which the Metal Man forces are directed they find it. What’s more, they also find the Master Metal Man who controls the rest, and who raises a number of additional questions about just what is going on on Venus: is the Master Metal Man also a robot? If not, why is he a giant? As a giant man, why does he appear to have crammed himself inside of a mid-sized building instead of, say, venturing out to crush Amazon resistance?

We never learn the answer to any of these questions, because it is at this point that someone flies Flint’s ship overhead and drops “floating split atomic bubbles” on the control station to blow it and the Master Metal Man to high heaven. Venus is saved!

Flint nearly becomes King of Venus before getting in trouble with his ladyfriend Mimi, who a guess must have been the one who nuked the control station and saved the day. (Planet Comics 008, 1940)