Super power

No superpowers in the original iteration of the character (comics have become really stupid recently so who knows if some one-off book gave him powers by now...comics are really stupid today)

Frank Castle was a USMC Vietnam vet who served as a sniper and a scout...not superhuman but a total badass for sure

He debuted in the mid 70s and was one of the first US comic heroes who killed with no mercy given...until then it was mostly 'tie up the robbers 'til the cops show up' stuff and that was getting stale...
Also, the US war in Vietnam had just ended poorly and a US President had made an ass of himself by the early/mid '70s
A 'hero' willing to cut through red tape and waste the dirtbags was very well recieved here in The States...frankly, ive loved The Punisher stories since the '80s but he should have been killed dozens of times by now...the fact that Frank Castle is still breathing is because we grant him the superpower of immortality...we NEED a Punisher to wipe out the freaks and geeks
And he's going to keep selling books!

Too bad he aint real huh?

Obviously he can take more punishment and heal faster than the average human. This means that he MUST possess some abilities, right? Well, not exactly. As far as I know, it’s never been alluded (certainly not in the Marvel Cinematic Universe or any of the movies) that Frank Castle has a secret superpower, not even in the storyline where he literally kills off every Marvel superhero with his arsenal.

Although being known as an average (highly trained) man has always been an important aspect of The Punisher, he is nevertheless a comic character who’s supposed to be tough as nails. So, in order for a superpowerless “hero” like him to survive everything he goes through (and occasionally face off against actual superhumans), they need to bend the rules a little. But yeah, he has no real powers.