Neither the humpbacked 747 nor the cherry-red public buses that crisscross London surpass the Big Mac as the world’s most famous double-decker. Ever since Jim Delligatti, who died Nov. 28 at 98, created the sandwich in 1967 at a McDonald’s franchise near Pittsburgh, it has been the flagship item of the global fast-food chain, selling more than a half-billion servings annually in the United States alone.

The Big Mac has been called the “Elvis of sandwiches,” the “Paul Bunyan of hamburgers.” It’s the solid-food equivalent of Coca-Cola, a totem of consistency instantly recognizable from western Pennsylvania to India, where cows are considered sacred by the nation’s Hindu population and where the Big Mac is made with mutton or chicken and called the Maharaja Mac. President Bill Clinton, the onetime ­burger de­vourer in chief, was known to indulge his “Big Mac Attack,” as one memorable advertising campaign described such cravings.

Mr. Delligatti’s creation, a sensation from the start, was the subject of a legendary advertising campaign in 1974. The inescapable jingle mirrored the essential excess of the Big Mac itself, making one word of its ingredients — “twoallbeefpattiesspecialsauce- lettucecheesepicklesonionsona-sesameseedbun” — and daring people to pronounce it. (A follow-up spot featured people struggling to master the tongue-twister.)

The sesame seeds atop the bun were the pièce de résistance, a simple but decadent touch that marked the sandwich’s status as the grandee on the McDonald’s menu. For the company, the Big Mac was a shot across the bow to Burger King’s Whopper, created a decade earlier.

The Big Mac became a baby boomer favorite, then a Generation X delight, then a millennial treat, and on it went, even as grass-fed, antibiotic-free meat ate into Big Mac’s primacy and McDonald’s sustained withering attacks from critics. The film “Super Size Me” (2004), in which documentarian Morgan Spurlock risks his health to subsist on McDonald’s for a month, and Eric Schlosser’s book “Fast Food Nation” (2001) found deep fault with many of the company’s products.

Marion Nestle, a New York University nutrition and public health professor, wrote in an email: “The Big Mac has had an enormous influence on American — and international — eating patterns, not all to the good alas. It’s become a synonym — the prototype, an American icon — for junk food.”

The Big Mac has become a Rorschach test in an all-consuming debate: Is it an emblem of life-affirming plenty? A comforting embrace of fat and salt? A waist-expanding public health hazard at 540 calories — or more? Is it American cultural imperialism in sandwich form?

From any perspective, Mr. Delligatti’s legacy amounted to much more than a meal. The Economist magazine began printing its annual “Big Mac Index” three decades ago, tracking the cost of the burger across the globe. “Burgernomics,” as the British publication dubbed it, has become a wry, easily digestible and much-cited measurement of currency values.

Mr. Delligatti conceived the burger in a simple effort to grow business at his franchises in western Pennsylvania. He thought that only a new item would do the job, but he said he faced resistance from a “very cautious” McDonald’s bureaucracy that did not wish to tamper with the success of the simple lineup of burgers, shakes and fries. They worried about the sandwich’s high price — 45 cents, twice the price of a cheeseburger.

He could proceed, he was finally told, but only if he used ingredients already on the menu. (He violated the order by acquiring oversize buns for his oversize burgers.) At his Uniontown, Pa., franchise, he spent weeks formulating the special sauce. He saw the dressing — often described as Thousand Island with a few twists — as the critical ingredient, the “big thing” that would distinguish his double-decker sandwich from culinary forebears.

The sandwich (29 cents with coupon) sold so well in Uniontown — with profits reportedly jumping by 12 percent — that Mr. Delligatti began to feature it at his other franchises. The company introduced it nationally in 1968, for 49 cents, and sold it under various names, among them the Aristocrat and the Blue Ribbon Burger. A young McDonald’s advertising department secretary, Esther Glickstein Rose, reportedly christened it the Big Mac.

The Big Mac became the chain burger by which all subsequent ones have been measured. But Mr. Delligatti, who spent some years in Southern California, acknowledged a debt to Bob Wian, who operated a Glendale, Calif., hamburger stand and crafted a similar double-decker burger in the late 1930s that became the signature item of Bob’s Big Boy restaurants.

“This wasn’t like discovering the lightbulb,” Mr. Delligatti later told the Los Angeles Times. “The bulb was already there. All I did was screw it in the socket.”

Michael James Delligatti was born in Uniontown on Aug. 2, 1918, and moved frequently in the area for his father’s jobs as a blacksmith, cobbler and confectioner.

After Mr. Delligatti’s Army discharge during World War II — he developed trench foot in Europe — he managed a drive-through restaurant in Newport Beach, Calif., and co-founded a casual eatery in Pittsburgh.

While attending a Chicago restaurant fair in 1955, he met businessman Ray Kroc, who was building the McDonald’s empire. Two years later, Mr. Delligatti opened his first McDonald’s in Pittsburgh. He owned 48 stores at his peak, gradually selling many of them back to the company.

At the time of his death, at his home in the Pittsburgh suburb of Fox Chapel, Mr. Delligatti owned two McDonald’s, and his family members ran more than two dozen more in Pennsylvania and North Carolina. He helped many employees become franchise owners and was also involved in Pittsburgh-area charities.

His first marriage, to Ann Vunora, ended in divorce. Survivors include his wife of 54 years, Eleanor Carmody Delligatti of Fox Chapel; a son from his first marriage, James Delligatti of Fox Chapel; a son from his second marriage, Michael F. Delligatti of Wexford, Pa.; five grandchildren; and eight great-grandchildren.

Culinary luminaries have staked varying positions on the Big Mac. Julia Child, a fan of McDonald’s fries, once said she disliked the sandwich because it was “all bread.” In New York magazine, food critic Mimi Sheraton suggested the toilet as the perfect repository for the sauce, which she called an “oily, sweet-sour emulsion.” Yet Michael Stern, the eminent food writer, told the Los Angeles Times that the Big Mac was a secret source of pleasure that, once a year, “really satisfies that primeval need.”

This year, McDonald’s began test-marketing bigger and smaller variations on the Big Mac — the Grand Mac and Mac Jr. — to keep up with competing market forces demanding more and less.

Mr. Delligatti, who also played an instrumental role in the creation of McDonald’s breakfast menu, did not receive a financial windfall from the Big Mac. “Everybody thinks I did,” he told the Pittsburgh Post-Gazette. “But no way. All I got was a plaque.”

He said he ate at least one Big Mac a week, noting that moderation was only common sense. His son Michael, echoing his father, said the Big Mac has been unfairly targeted for criticism. “You go to high-end restaurants and get the lobster bisque,” Michael Delligatti said, “that’s way more calories than a Big Mac.”