Big Mac creator Michael "Jim" Delligatti attends his 90th birthday party in America. Picture: AP.

Michael James “Jim” Delligatti, the McDonald’s franchisee who created the Big Mac nearly 50 years ago and saw it become perhaps the best-known fast-food sandwich in the world, died on Monday at home in Pittsburgh.

Delligatti, who according to his son ate at least one 540-calorie Big Mac a week for decades, was 98.

Delligatti’s franchise was based in Uniontown, not far from Pittsburgh, when he invented the chain’s signature burger in 1967 after deciding customers wanted a bigger sandwich.

Demand exploded as Delligatti’s sandwich spread to the rest of his 47 stores in Pennsylvania and was added to the chain’s national menu in 1968.

Michael "Jim" Delligatti sits behind a Big Mac birthday cake at his 90th birthday party. Picture: AP.Source:AP

“He was often asked why he named it the Big Mac, and he said because Big Mc sounded too funny,” his son Michael Delligatti said.

However, McDonald’s in 1985 honoured Esther Glickstein Rose with coming up for a name for the burger and presented her with a plaque etched with a likeness of the best-selling sandwich and french fries between the Golden Arches.

She was a 21-year-old secretary for the company’s advertising department in 1967 when, the story goes, a harried executive dashing to a board meeting asked her for a name nomination.

Jim Delligatti’s family disputes that Rose came up with the idea. The company didn’t immediately clear up the dispute when contacted on Wednesday.

The iconic Big Mac is known for its stacked patties and ‘secret sauce’. Picture: AFP.Source:AFP

Delligatti told The Associated Press in 2006 that McDonald’s resisted the idea at first because its simple line-up of hamburgers, cheeseburgers, fries and shakes was selling well.

“They figured, why go to something else if (the original menu) was working so well?” Delligatti said then.

McDonald’s has sold billions of Big Macs since then, in more than 100 countries.

When the burger turned 40, McDonald’s estimated it was selling 550 million Big Macs a year, or roughly 17 every second. Delligatti received no payment or royalties for coming up with the burger, the company said.

“Delligatti was a legendary franchisee within McDonald’s system who made a lasting impression on our brand,” the Oak Brook, Illinois-based company said in a statement.

The Big Mac “has become an iconic sandwich enjoyed by many around the world.”

According to McDonald’s they haven’t changed the size of their legendary 540 calorie burger since 1971. Picture: Supplied.Source:Supplied

Ann Dugan, a former assistant dean of the University of Pittsburgh’s Katz School of Business and an expert on business franchises, said Jim Delligatti’s genius was simple: He listened to customers who wanted a bigger burger.

“In franchising, there’s always this set playbook and you have to follow it. Jim saw an opportunity to go outside the playbook because he knew the customer,” Dugan said.

“He persevered and (McDonald’s) listened, and the rest is history.”

In addition to his two sons, Jim Delligatti is survived by his wife, Ellie, five grandchildren and eight great-grandchildren.