Lots of superheroes are “children of the atom” in the sense that they derive powers from some sort of radioactivity (think Spiderman or Hulk or even Daredevil) while others are just born with powers without explanation (X-Men, Thor, Superman, Aquaman, Wonder Woman).
Who is a superhero that is somehow grounded in reality, meaning that they could “potentially” make sense (either their origin story is believable, even if it has some obvious gap to make a super power happen, or their power is somehow limited or constructed in a “reasonable” way).
I guess with these restrictions, Batman would be OK since he’s got no superpowers, but he’s insanely rich and therefore can both train himself and have access to sophisticated gadgets, but can you think of less obvious ones (even if they’re minor characters)?
Thanks for reading this!
Edit: thanks for all the answers and apologies for the slow replies. I’ve had a couple of complicated days. I’ll now go through answering you. Several people made me realize I hadn’t been precise in what I meant and helped with their answers. I was looking for superheroes or superpowers that are somehow “believable” in that they’re either constructed in an unexpected way or in a way that you could almost accept as plausible
There are many that are results or accidents from experiments. The Flash got his powers from a lab accident. Iron Man’s suit is part of his own research. Cyborg from Teen Titans was an experiment from a father trying to save his son. Elonging Man did “a life research on yogi’s elasticity” to create a potion that gave him his powers. Plastic Man was also an “accident” with an unidentified chemical.
Ghost Rider and Spawn made deals with the devil to get powers. Spawn even has an actual limit on how much he can use his hellish powers
These are all great answers. As discussed in another answer to a comment (the one on Poison Ivy and Mr Freeze), I agree that “believable” experiments gone wrong based on actual science provide a source of “believable” super powers.
On the other hand: Ghost Rider and Spawn have really nice origin stories which also place restrictions on what they can do not to make the characters god like.