Karl 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, has died.

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.

Lagerfeld became a god-like figure in the fashion industry during his more than three decades at Chanel.

New York Times fashion editor Vanessa Friedman told Mike Hosking he turned it from a struggling label to a global luxury brand.

"He took over Chanel as a young, upstart designer...it was a relatively fusty state house that was surviving on the back of its perfume business and he completely reinvigorated it."

"He is responsible for much of what we think of as the modern fashion world."

"What Lagerfeld did was create a model for how to be a designer that become the standard in luxury."

She said he was an omnivorously curious person and talking to him was fascinating and surreal."

A freelance designer for Parisian ateliers and fashion houses in the 1950s and 1960s, 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 Chloe.

In 1983, he was hired by Chanel as chief designer to modernise 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, 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 colours. He refashioned the house's iconic quilted handbags in leather and its trademark tweed jacket in terry cloth and denim and candy-coloured 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.

"I play with Chanel's elements like a musician plays with notes. You don't have to make the same music if you are a decent musician," he told Vogue magazine in 2010.

He also made the fashion house accessible and desirable to younger buyers by introducing ready-to-wear clothing and revamping the brand's accessory lines.

Fashion historian Valerie Steele said the average age of a Chanel customer during Lagerfeld's tenure dropped from the mid 50s to the late 30s. "In effect, he performed emergency surgery and totally revivified the brand," Steele told the Washington Post. "He made it completely relevant and contemporary again and has continued to do so, against all odds."

Time and again, he was able to drum up excitement and demand for Chanel's clothes despite recessions, bubbles and bursts. In 1997, Vogue crowned him the "unparalleled interpreter of the mood of the moment."

His success inspired what former French Vogue editor Joan Juliet Buck deemed "the Lazarus movement" in fashion - a business model of hiring up-and-coming designers to make over age-old fashion houses. Examples include Gucci's hiring of Tom Ford and Louis Vuitton's hiring of Marc Jacobs.