Miuccia Prada

If I had to choose the most influential designer of the 1990s, it would be Miuccia Prada. She wasn't the loudest or the most glamorous, but she changed what luxury fashion could be, and a remarkable number of later trends trace back to her.

She came to fashion from an unusual direction. The granddaughter of Mario Prada, who founded the Milan leather-goods shop in 1913, she earned a doctorate in political science, was involved in left-wing politics in the 1970s, and trained as a mime. She joined the family business in the 1970s and took over in 1978, working with her future husband, Patrizio Bertelli, who ran the business side. At that point Prada was a respected but old-fashioned maker of luggage and bags.

Her first big idea was about material. From the late 1970s she began making bags - and, from 1984, backpacks - from a tough, industrial black nylon instead of leather, labelled only with a small triangular metal logo. It was an odd, almost anti-luxury choice, and by the early 1990s the black nylon Prada bag had become one of the most desired status objects in the world. Ready-to-wear collections followed from the late 1980s, and the younger, more playful Miu Miu line - named after her own nickname - launched in 1993.

Through the 1990s, her clothes were deliberately complicated. They were often simple in shape, in line with the minimalist mood, but she mixed in unexpected references: prim 1950s and 1960s shapes, school-uniform details, technical fabrics, and colours that seemed slightly "wrong." Her spring/summer 1996 collection, with its brownish, olive, and mustard retro prints, was nicknamed "ugly chic," and it made the idea of deliberately awkward taste fashionable. She also launched a sportswear line, Prada Sport, with its distinctive red stripe, toward the end of the decade.

What I admire most is that she treats fashion as a place for ideas. Her clothes ask questions about good and bad taste, about what's feminine or sexy, and about what luxury means, and they often look strange before everyone copies them. The idea that clothes can be clever, even a little uncomfortable, rather than simply beautiful, owes a great deal to her 1990s work.