I posted a version of this over on the DC board -- but that one was only asking for answers from DC's continuity. Now I'm asking a Marvel-specific version of the question!
How many times have we seen characters from subatomic cultures debut in Marvel comic books?
I can rattle off a few examples right away. For instance:
1. Marvel used to publish a licensed "Micronauts" series. The title characters had all been born and raised in the "Microverse" -- meaning each person was (in his "natural" size) much smaller than a typical atom! They managed to get big enough to be about "action figure-sized" as they ran around on Earth-616 for awhile, however.
2. The Fantastic Four's enemy Psycho-Man originally came from such a setting. (Although I remember that in the 1980s his OHOTMU entry would say it had later been scientifically determined that he actually came from another dimensional reality -- instead of literally just making himself much bigger or much smaller as he moved from his homeworld to the FF's Earth and back again. But that was only a belated retcon, right?)
3. Back in the 1970s: Jarella, a princess of the subatomic kingdom of K'ai, was madly in love with The Incredible Hulk. (Then she died tragically, of course.)
I'm sure there have been other examples of characters with subatomic backgrounds. Anybody care to take a stab at dredging some of them up from memory?