Weird humanoids as far as the eye can see!
Demon People:
The Demon People are seemingly native to the dimension that Breeze Barton travels to in his first adventure and are in conflict with Miracle City and its population of immortals. Even though their major goal is to get through the dimensional aperture and invade Earth, I would have a lot more sympathy toward them (eternal neighbours really must be the greatest test a people could have, after all) if they weren't also huge slavers. I do really like the one big wing/fin that they have on their back, even if I can't figure out what it could be for. (Daring Mystery Comics 003, 1940)
Jupiterians:
The Jupiterians, or more specifically the South Jupiterians, are a peaceful, swamp-dwelling people who want to live somewhere other than a swamp and have thus decided to enter into a colonial relationship with Earth. And it works! Against all historical precedent, the South Jupiterians are soon the proud owners of a new city called New Washington! No strings attached!
The real threat to South Jupiterian sovereignty comes in the form of a diplomatic envoy of lop-eared North Jupiterians under the command of Princess Eelo (whose own long ears are presumably concealed under that kicky headscarf). They represent the bad kind of colonialism, in contrast to the warm fuzzy colonialism of Earth under Captain Nelson Cole, and it takes a plague scare and the complete destruction of New Washington to shift them. Back to work, South Jupiterians! (Planet Comics 009, 1940)
Link People:
Comics and other genre fiction are of course chock full of speculative missing links, but the key thing about the missing link concept is that it represents the bridge between ape and human. The idea that the missing link is instead some sort of humanoid reptile that just kind of ignores the existence of mammalian evolution and instead posits (I think) a chain of reptile -> reptile-man -> ape -> human is very weird!
This being a comic book, such a wild speculation by a collection of white-haired scientists is of course 100% accurate, down to the location and architectural style of the Link Person community. Among other things, this means that the Descent of Man image is going to have to be heavily revised, and also that diver Kinks Mason is immediately sent in to bother this untouched society.
Fearing that a mere photograph will not be believed, the scientists opt to kidnap one of the Link People, thus completing their introduction to humanity via a whirlwind of violence, death and loss (okay, they do try to sacrifice some of the scientists to their gods, but I think that they might have been justified). (Fight Comics 005, 1940)


















































