Kenneth Jay Lane's bachelor apartment in 1970 is full of Russian cigarette boxes, Oriental antiques and statuary. (Neal Boenzi/New York Times)

Kenneth Jay Lane, the king of costume jewelry who revolutionized the fashion industry in the 1960s with his realistic replications of priceless gems, died July 20 at his home in Manhattan. He was 85.

The cause was a heart attack, said Chris Sheppard, the executive vice president of Kenneth Jay Lane Inc.

A designer who preferred the term inventor, Mr. Lane charmed the fashion elite and the American middle class alike with his inexpensive, near carbon copies of costlier creations. By 1975, his company had 2,000 stores worldwide.

His devoted following of movie stars, political spouses and members of European royal families made him one of the most well-connected men in New York City.

The Duchess of Windsor was buried in a Kenneth Jay Lane faux emerald snake bracelet, per her request. Elizabeth Taylor reportedly called KJL, as Mr. Lane was affectionately nicknamed, from Leningrad to custom order reproductions of diamond jewelry she already owned. Former first lady Jacqueline Kennedy Onassis was also a customer.

Designer Carolina Herrera and jewlery designer Kenneth Jay Lane in 2004. (Thos Robinson/Getty Images)

Even Mick Jagger of the Rolling Stones was “buying up belly chains by the bushel” from the designer for his concerts, People magazine reported in 1975.

Mr. Lane favored the flashy and whimsical, pairing leather with tweed, alligator and cobra skin and pavé diamonds. He sold bedazzled flamingos and diamanté Maltese crosses alongside yards of faux pearls.

The unapologetically gaudy, eccentric pieces quickly became Mr. Lane’s calling card. He would refer to them as “faque” (fake) and as “junque” (junk), probably in the posh, nonchalant inflection he was known for that concealed his Detroit upbringing.

Mr. Lane’s upper-crust clients and average American consumers alike shared their enthusiasm for his jewelry. Plastic, rhinestones, glass and other manufactured materials were used in his collections.

“They were very good, flamboyant styles,” said Valerie Steele, the director and chief curator of the Museum at the Fashion Institute of Technology in New York. “They were affordable, yet they were such well-done pieces that they attracted higher-end clientele.”

Many of Mr. Lane’s pieces were obvious copies of designs by Cartier, Van Cleef & Arpels and other ritzy jewelers. In his hands, they were renovated to a more modern, less delicate, yet nevertheless striking shape. He once joked that he designed with a photocopier, Scotch tape and a pair of scissors.

Yet he occasionally drew inspiration from elsewhere, such as his far-flung vacations. A trip to Peru later manifested itself in his work in the form of “vaguely Inca-inspired” masks that he later sold, in 1967, for $260, or about $1,900 in today’s dollars.

His company pulled in profits from the boutiques, but Mr. Lane’s monthly QVC appearances at one point could reel in $300,000 an hour. He once sold out of three hundred samurai sword watch pins in four minutes. The designer partnered with the ubiquitous home shopping channel for more than 20 years.

The “fabulous fake,” as he playfully referred to himself, also worked at times with genuine gems, a sideline project that was nevertheless a lucrative addition to his portfolio. Mr. Lane signed a contract with a wholesale jeweler in 1967 to develop a line of gold jewelry with precious and semiprecious stones, priced at $50 to $500.

“I’ve been designing for secure ladies,” he told the New York Times in 1967. “Now I’ll be designing for insecure people who need something real.”

Mr. Lane’s domestic design taste was expectedly eccentric.

He once lived in the Murray Hill neighborhood of Manhattan, in an ornately decorated residence that the Times once described as an “extremely tasteful version of the Austin Powers era.”

Rare books lined the walls. His master bathroom was completely lined in mirrors. The home was stuffed with memento mori, among them skulls carved out of ivory and alabaster as well as a 16-inch-tall bronze skeleton. The dining room was lined with fabric, making it appear like a Bedouin tent.

Mr. Lane was born in Detroit on April 22, 1932. He graduated from the Rhode Island School of Design in 1954 and got a job in Vogue magazine’s art department. Within a few years, he was designing shoes for Christian Dior.

Early in his design career, he was known for working 18-hours days. To save money on administrative costs, he would file his own invoices and packages, all the while whipping up new designs.

“I was understaffed and underfinanced because I didn’t want outside help,” Mr. Lane told The Washington Post in 1967. “I’d go to dinner parties and come back and work the rest of the night in my black tie.”

At 40, he married Nicola Weymouth, an Englishwoman almost two decades his junior, known for her bright red hair and friendship with art world giants like Andy Warhol, who once made her the subject of a portrait.

The marriage ended in divorce within two years, with Weymouth absconding to England after a “civilized” divorce party thrown in their honor. They reportedly remained on good terms, with Mr. Lane saying that his ex-wife was simply an “unexportable Englishwoman [who] couldn’t keep a horse and garden in New York.”