Paris is a place for revolutions: the sci-fi fantasies of Cardin and Courrèges, Jean Paul Gaultier’s skirts pour homme and the inflated gothic rituals of Rick Owens. All wild, memorable and museum-worthy. But it may be Agnès Troublé who has changed what we wear today, more so than any fierce iconoclast.

When she introduced Agnès b. in 1975 (the b is for Bourgois, Ms. Troublé’s married surname), many women, including the designer’s mother, were still having their clothes made to order. It was not always haute, but it was still couture. Yves Saint Laurent had introduced prêt-à-porter in 1966, but it was Ms. Troublé who moved the needle in the next decade, making cult clothes that were bon chic, bon genre, easy to wear and off the rack.

“I always just wanted to create for every man, woman and child,” Ms. Troublé said via a video call from her studio in Paris. “My philosophy comes from what happened on the streets of Paris in 1968. And I still design everything myself.”

When Agnès b. began, 50 years ago, it was fresh, cool and totally Parisian. Inspired by Ms. Troublé’s flea market finds, it was aligned with the art world and 1960s cinema and sold at a more accessible price than Saint Laurent’s Rive Gauche. It was where you went for the perfect striped top, white shirt or black pants, and it created the model for dozens of midrange French fashion labels.

Without the 83-year-old Ms. Troublé, there would most likely be no A.P.C., Comptoir des Cotonniers, Maje, Sandro or Sézane. Fifty years after she founded it, her business remains family owned, with 242 stores globally. She has sold more than two million snap-button cardigans and opened her own contemporary art gallery, La Fab, in Paris in 2022, showcasing pieces from her personal collection of more than 5,000 works.