Giorgio Armani, a designer who rewrote the rules of fashion not once but twice in his lifetime, has died. He was 91.

His death was confirmed on Thursday in a statement by Armani Group.

A reluctant designer but an instinctive empire builder, Mr. Armani initially became a household name by adapting a custom from traditional Neapolitan tailors: softening the internal structure of a man’s suit to reveal the body inside. Simply by removing shoulder pads and canvas linings, Mr. Armani devised what in the early 1980s became a new male uniform, the easy and almost louche sensuality of which soon enough found favor among a female clientele.

“All the women of my generation, including Hillary Clinton, were wearing jeans in the 1960s,” said Deborah Nadoolman Landis, a costume designer and historian. and founding director and chair of the David C. Copley Center for Costume Design at the University of California, Los Angeles. “But where do you go from Woodstock? How do you professionalize that look when those women start entering the work force? You professionalize it by wearing a feminized suit from Armani.”

Androgynous, luxurious, positioned somewhere between the stuffy establishment attire popular among male executives at the time and the prim skirt suits favored by many professional women, Mr. Armani’s designs offered an alternative form of power dressing.

For a time, in Wall Street corner offices, Madison Avenue boardrooms and the executive suites of many Hollywood talent agencies, an Armani suit was the default uniform of authority, an occupational armor rendered in crepe or cashmere and cast in a somber palette from which the designer would seldom stray.