Like most things, it was great when it first began and there was no official term for it, no commercialism, no 'scene', no sub-culture, or anything like that. At it's height, it was mostly Star Wars fans dressing up as Stormtroopers, with some Jedi, Ghostbusters, Aliens and a few such others on the periphery. It was mostly adults, mostly about geek-mates getting together for a drink (OK, lots of drinks), celebrating their fanship of whatever film/series, meeting the cast and crew (who were often delighted to be involved, like the above-mentioned Terry English), and mostly just being social... mostly.
Somewhere along the line it became all about jailbait kids dressing as Japanese schoolgirls, and creepy Anime/Manga incel manchildren trying to finger them in public or at least take photos up their skirts, all with a heavy commercialist overtone from the near-monopoly of the event organisers.