the first concept of popular culture was invented with the "discovery" of the folk in the late eighteenth century and in the folk-lore and folk-song movements of the nineteenth and early twentieth centuries.
Over a period of about 140 years the idea of popular culture as folk culture was developed by intellectuals across Europe and the USA. They had not set out to produce a way of thinking about popular culture, but in doing what they did- whether this was seeking to promote national culture or to develop a science of "primitive man" - the first concept of popular culture was invented.