You simply cannot have comic book adventures without a few aliens creeping in around the edges. It’s science.

Monkey-Men:

These Monkey-Men are encountered by Congo Bill while searching for a long-lost explorer named Desmond in the deep dark jungle. There’s not much to distinguish them from other the other ape-people we have encountered thusfar, aside from the fact that they live in cool-looking cone-shaped houses.

The missing Desmond of course turns out to be an amnesiac who is living with the Monkey-Men as their leader – evidently a beard makes all the difference to the apish eye. Bill and his pals manage to extract Desmond from this situation without wantonly slaughtering the entire village (a real measure of restraint in a jungle explorer in my experience), so the Monkey-Men are potentially haunting the wilds of Earth-Two to this day. (More Fun Comics 060, 1940)

Plantmen:

These very neat-looking ambulatory plants are discovered in a cavern under Pennsylvania by child prodigy Marvo 1￮2 Go+ in the year 2680. Unusually for such a weird-looking Golden Age nonhuman species, they are completely friendly. There is, however, no indication that friendly relations were established between the surface world and the Plantmen, and indeed Marvo’s first move upon getting home is to siphon off the cavern’s tropical atmosphere to give Pennsylvania a permanent summer climate, which I can only hope isn’t disastrous to the underground ecosystem. Maybe you should have crushed him when you had the chance, friend. (Superworld Comics 002, 1940)

Plutoks:

These stoic residents of the planet Pluto must make a pilgrimage to a planetoid inside of the orbit of Mercury every year in order to “bake” themselves and store up enough internal heat to survive. It seems like a hard life, made harder by the fact that oafish Earthman Cosmo Corrigan has been assigned to establish a space base on Pluto. (Planet Comics 009, 1940)

Plutonians:

Speaking of rough times on the then-planet Pluto, this society of bald kilt-wearers really takes it on the chin at the hands of the evil Quorak and his magnetic ray. They are saved from total extermination by the Inter-Planetary Police, but not before taking a real kicking. (Planet Comics 001, 1940)