They say "Never judge a book by its cover.", and with good reason: some interesting books have dull covers, dull books have interesting covers, and sometimes the cover may be entirely nonsensical. This can also apply to movies, where minor characters get prominently featured due to their actor getting very popular later on. How this applies to comic books however can be... well, we'll get to it.
Jetman was by day a... well, we don't know his backstory. By night, however, he was Jetman, a flying superhero dressed in red! In his adventures, he'd... well, okay, he didn't have any adventures. Yet he featured in nearly 30 issues of Jetman comics... sort of. You see, Jetman existed on the cover of this series and nowhere else.
You might think it's a bit odd for there to be a cover-only superhero since surely a comic would want to show off its own marketable heroes like... well, I don't know what heroes feature in these comics, which is part of the problem here. Apparently though it was surprisingly common for comics to be sold with heroes that only ever exist on the cover, never getting to be a part of the contents. Why, there's the Human Fly, Liberty Man, Green Light, Liberty Boy, Stellar Man, Miss Liberty, and how can we forget the villainous Skeleton Key (who dresses like the Blue Beetle and holds a key with a skull on it evilly)?
The most fortunate part of this, I suppose, is that there's no lore to be contradicted here. These cover-only characters can be made into whatever you want (which, granted, you could do that with public domain superheroes anyway, but still).