I hit the Wikipedia page "popular culture" by mistake, and there is a picture of Elvis, whom I despise, and because I could not reconcile the fact that he is, indeed, unequivocally, the first instance of popular culture with my revulsion for everything that he stands for, it set me thinking. Perhaps pop culture existed in the 19th C too? Well, yes, but it was not called that. So what is different about that from what we call pop culture?
And the answer is obvious: all mainstream terms are an attempt by the ruling class to contain society, to box it in. Anything that deviates from their plan has to be belittled by making it separate. So, the health and fitness movements of the 19th C weren't given a name; they were perfectly fine with the ruling class, and might have been populated mostly by the ruling class also. Rock and Roll was hideously mainstream; white folks singing black songs, but it was still a crack in the wall. A crack that opened up a hole through which poured every element that would make a modern society, if the ruling class would ever let it. But no, of course they just put another wall around it. More names. More control.
And Elvis, the anaemic, sneering, smart-ass hillbilly, is the perfect symbol as well of how the mainstream only lets through what cannot harm it. Because of Elvis, the Red (Republican) South was assured. It was inevitable. The wall was assured, the rule secure.