Mr. Lundgren with Billy. (Sandra Werud/Inter IKEA Systems B.V.)

Gillis Lundgren, an industrial designer who helped make Ikea the largest furniture retailer in the world with his no-frills designs, most notably the Billy bookcase that millions of frugal book collectors have used to build their home libraries, has died at 86.

Kajsa Johansson, an Ikea spokeswoman, confirmed his death, describing him as “a man full of ideas that he quickly turned into practical products,” but gave no other details. Quartz magazine reported in an online obituary that he died Feb. 25.

Founded in the Swedish countryside in 1943, Ikea grew from an all-purpose, low-cost retailer for farmers into a corporate behemoth with 328 stores in 28 countries and a reported $35.7 billion in sales in fiscal 2015. Its founder, Ingvar Kamprad, who began his career as an enterprising teenager peddling mail-order nylon hosiery and udder balm, is today one of the richest men in ­business.

Mr. Lundgren joined Ikea in 1953 as the company’s fourth employee and advanced to become its first design manager. A draftsman with training in graphics, he designed hundreds of Ikea’s simple, portable furnishings and was credited with creating the company logo, whose blue and yellow colors were taken from the Swedish flag.

Ikea announces itself along roadways with the apparition of its mammoth warehouses, also blue and yellow, and in the mail with the arrival of its nearly warehouse-size catalogues. Every year hundreds of millions of shoppers — new students and new graduates, new tenants and new homeowners, the newly married and the newly divorced — trek into Ikea stores in pursuit of the economical establishment of a household.

“Ideas are perishable,” said Mr. Lundgren. (Ikea)

Although few of those people are likely to know Mr. Lundgren’s name, all of them are or will soon become acquainted with perhaps his most significant contribution to the Ikea business model: “flat-pack” furniture.

Ikea was not the first company to employ the now-ubiquitous system, but Mr. Lundgren was credited with perfecting it for Ikea’s purposes. He said the idea came to him early in his career. Ikea had recently entered the furniture market, he recalled, and “storage space became an issue.”

“When I looked at how we might keep a large number of these tables at our low price,” he told the London Independent, “I thought: ‘Why not take off the legs?’ ”

Today, shoppers peruse fully assembled Ikea wares in showrooms and on the company’s website but take home (or order for delivery) boxes that contain the products in pieces, neatly stacked, to be assembled on arrival. The flat-pack system allows Ikea to save money by moving its products more efficiently and customers to save money, although not time, by providing the labor.

To instruct customers in assembly, Ikea prints wordless, illustrated manuals featuring cartoon-like figures at work. Those figures do not appear prone to the frustrations involving stripped screws or missing parts that have helped turn the Ikea clientele into a quasi-fraternity.

Many shoppers who enter an Ikea warehouse, no matter how few their belongings or how small their home, have at least a few books to place on a shelf and at least one wall against which to rest it. Those shoppers may not, however, have a large amount of money to part with. And so they may go home with a Billy bookcase, created by Mr. Lundgren and introduced in 1978.

He was said to have drawn the design on a napkin.

“Ideas are perishable,” he once remarked, “and you have to capture the moment as soon as it arrives.”

Billy’s plain shelves of varying heights and widths proved imperishable and remain largely unchanged from Mr. Lundgren’s original design. Because of improvements in production efficiency, the product line costs less today than it did at its debut, with one basic model on sale for $69.99.

“I want to create solutions for everyday based on people’s needs,” Australian newspapers quoted him as saying. “My products are simple, practical and useful for everyone, no matter how old you are or what your life situation.”

Gillis Lundgren was born in Lund, in southern Sweden, in 1929. He studied at the Malmo technical college and joined Ikea as a catalogue manager. A complete list of his survivors could not immediately be confirmed.

He was credited with designing or helping design the vaguely mid-century modern Klippan sofa and Lövbacken table, originally sold in the 1950s under the name Lövet.

Ikea product names, with their profusion of umlauts and unfamiliar sounds such as Ektorp Jennylund (a chair) and Magnarp (a lamp), are the subject of cult fascination. (The company’s name is an acronym made from the initials of its founder, I.K., followed by the first letters of the names of the farm, Elmtaryd, and the town, Agunnaryd, where he grew up.)

The Billy, one of the simpler words in the Ikea lexicon, was reportedly named for Billy Liljedahl, an advertising colleague of Mr. Lundgren’s who had expressed a desire for a “bookcase just for books.”

According to Quartz, Ikea produces 15 Billy bookcases per minute and had sold more than 41 million sets by 2009, after Billy turned 30 — the age at which some Billy owners may choose to graduate to a higher-end library. Many used Billy bookcases find their way to new homes, by way of Craigslist or as family hand-me-downs.

“I’m particularly happy that Billy has made it possible for so many people to build their own little library,” Mr. Lundgren once said. “In the old days, books were quite uncommon in most homes. These days, everyone has books, which is as it should be.”