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