Karl Otto Lagerfeld, a German-born couturier whose reinvention of the luxury fashion house Chanel made him one of the most well-known and influential fashion designers of the late-20th century, died Feb. 19.

Chanel confirmed his death, according to the Associated Press. Other details — including his exact age, which was long the subject of mystery — were not immediately available. The AP reported that he was approximately 85.

With his crystal white ponytail and dark sunglasses, Mr. Lagerfeld was an instantly recognizable fixture in the orbit of fashion and popular culture.

Often called Kaiser Karl among peers and the fashion news media, he was the creative force behind some of his industry’s most recognizable and profitable luxury brands. Most recently, he served simultaneously as head designer of Chanel, the Italian fashion house Fendi and his own eponymous brand.

Despite being almost twice the age of his fashion competitors in recent decades, he continued to produce collection after collection for his various labels — sometimes more than 15 times annually. It was an exceedingly prodigious output, and he drew mostly favorable reviews.

A freelance designer for Parisian ateliers and fashion houses in the 1950s and 1960s, Mr. Lagerfeld was an early pioneer of the women’s ready-to-wear movement and built his reputation in the fashion industry with his mold-breaking designs as creative director of Fendi and the French label Chloé.

In 1983, he was hired by Chanel as chief designer to modernize the fashion house a dozen years after the death of its founder, Coco Chanel. When he took over, the house was floundering and barely surviving off its perfume sales. “Everybody said, ‘Don’t touch it. It’s dead,’ ” he told New York magazine. “But when people said it was dead and hopeless, I said it was interesting.”

As head designer, Mr. Lagerfeld reinvigorated the luxury brand and grew it into a multibillion-dollar fashion enterprise while maintaining Chanel’s tradition of craftsmanship and quality.

He was able to reinterpret the label’s signature pieces in flamboyant and fresh cuts and colors. He refashioned the house’s iconic quilted handbags in leather and its trademark tweed jacket in terry cloth and denim and candy-colored hues. He also broke Coco Chanel’s above-the-knee taboo, introducing shorter, more modern hemlines and Chanel’s first miniskirts. In doing so, he was able to recapture the brand’s youthfulness.