The brand that lived
The managing director of the Licensing Industry Merchandising Association nails it in a guest piece for Campaign:
Harry Potter is more than the films, more than the books. It is a genuine lifestyle brand.... Along the way its brand DNA has grown to encompass imagination in all its infinite possibilities, outdoing conventional fashion brands at their own game.
I've argued in the past that Batman, Superman, Spider-man are all t-shirt brands with comic book spinoffs. I think Harry Potter belongs in that pantheon as well: geek culture brands where the identification is now so embedded that they're part of the visual vernacular. It isn't just about a nerd franchise being in Primark, it is about a nerd franchise being in Primark and coverage in the Sun.
If anything, Harry Potter's gone a step further and given us four lifestyle brands. Superhero logos say, generously, something about you. But the four Hogwarts houses have become a socially-accepted Meyers-Briggs self-classification.