Most memorable older It Girls? 28
The result is only visible to the participants.
...that changed Kpop and the entertainment industry forever?
During their IT Girl days, Jessica and then Krystal invented and popularised the ice princess thing. 
They made it chic and Jessica did the same for airport fashion. Before her, it wasn't a thing and now it's everything.
Yoona made the gg centre a thing and changed the game forever. There were many visuals before her but she was the first ever face of the group and centre and she went on to endorse a ton of brands and now it's a thing.
GD and Snsd invented full on modeling careers for idols. While GG owned the fashion game as an idol, Snsd and some of it's members were busy cover girls for all top magazines around Asia and now idols and fashion and cover girls are a major thing.
Bonus:
Irene is the original visual of them all. 
Edit: I made this thread just so you can talk about your favs, so instead of complaining about how I've not mentioned them, please mention and talk about them, their inventions and influencing power. 
