Superheroes

For the most part, Americans tend to venerate figures from scripture (Moses, David) or real life people who had achieved mythic status (Davey Crockett, Johnny Appleseed), with a few characters from tall tales or acclaimed literary works, usually because of efforts by scoutmasters and tutors. However, it's hard deny to the influence comic books have had on American culture. This is largely because of their distinctive visuals, and because comic books (and comic book-inspired works) were the easiest to enjoy in a post-industrial society. They're portable, don't require electricity, can be  enjoyed at least a little bit by the illiterate, and can exist for a long time. Not permanently,  of course, but their impact lasted. Actually, in New Mexico, where the climate is drier and the Bible is much less popular, even the less widespread comic book characters like Green Lantern and the Fantastic Four are known, but for most of the continent, there are only a few who have managed to remain iconic for a thousand years.

Superman, of course, still exists in folklore, being the embodiment of America as a culture. He has his litany of superpowers, and even a few new ones. When updated to recent times, Clark Kent is a mid-mannered churchman or friar, usually with a hood covering his face. Lois Lane doesn't recognize him because she never looks him in the eye. The biggest difference is, in the Non-Denominational world, he's from Ohio valley, as opposed to Kansas, which is full of barbarians and heretics. It makes sense, as his creators were from Cleveland, and the Hall of Justice resembles Cincinati's train station.

Spiderman is maybe the most popular character from a storytelling perspective. He's distinctive and yet simple enough to be used for toys, puppets, and acrobats are known to dress in Spiderman costumes. "With great power comes great responsibility" is the peasant's answer to chivalry. Peter Parker's dayjob involves weaving tapestries, which his spider powers make surprisingly easy. Some people believe he was real, and friends with Barack Obama, so whether he's considered whimsical or sinister depends on that part of country's opinion of him.

Wonder Woman largely became popular because the combination of classical mythology combined with American iconography and a little bit of Nazi-punching (Americans are vague about World War II, but they know they crossed the sea to fight them) makes her a natural myth. Various kingdoms try to put their own nationalist spin on her, but because primary colors, stars, and eagles are on so many flags, the changes are usually subtle. She's considered so sacrosanct it's considered bad for prostitutes to dress like her, even though it's quite popular for brothels to have folklore themes.

The Incredible Hulk is maybe the former comic book character most popular with the nomadic herdsmen. They see him as the ultimate expression of pastoralism, a big green force of nature who smashes the corrosive and oppressive structures of the so-called "civilized" world.

In some cases, characters have gone beyond folklore, and have become somewhat de-fictionalized. These are naturally the comic book characters who generally didn't have superpowers.

In the original middle ages, it was common for errant knigths to blacken their armor to prevent rust and maybe do some extra-curricular battle, and real black knights started to appear in America. That many languages have the same word for "black" and "dark" didn't escape people, and so the idea of real life Batmans started occurring. In the middle ages, peculiar costume flourishes were pretty normal (It makes you easier to recognize on the battlefield, and may show off you wealth), so a couple people started using Bat-sigils on their coat of arms, and wearing the cowl when possible. Funny enough, "Robins" also became common, as sort a sort of cross between a squire and a herald. It should be also be said that at some point, bandits started to wear clown makes or makeup, but this may or may not have been inspired by the Joker. In any case, this practice caused clowns to be banned across the territories.

There's also a few real life Captain Americas, though it may have been an accident at first, with soldiers, especially in United States territory, having the combination of mail and start-spangled attire drawing comparisons, with some deciding to lean into it. The iconic captain America shield is very popular, and as a symbol is common on coats of arms.

Because of its popularity with real life military culture figures like Chris Kyle, the Punisher's ominous skull logo has also become very common among non-nonsense warriors, and a skull ring is even given to a warlord's personal executioner.

Thor is also a popular figure in Medival American legends,  held back in popularity only by the nervousness of liking a pagan creation too much. Because he was actually around in the middle ages, he fits in this era just fine. And because he was a staple of American comic books, he fits in with stories about Superman and Spiderman just fine as well. It's very popular in taverns to argue which muscelman can beat which in a fight.