Jim Delligatti took two years to convince McDonald's that the Big Mac was a good idea but 40 years on he takes pride in having invented one of the world's most widely eaten foods that is getting its own museum.

In 1967, the McDonald's franchisee got permission from the corporate office to put two beef patties on a hamburger bun.

Only a year later, the Big Mac he lobbied so hard for had made it onto the menu of every McDonald's restaurant in the United States.

"I felt that we needed a big sandwich," said the 89-year-old Delligatti, who has run McDonald's restaurants for more than 50 years. "But you couldn't do anything unless they gave you permission."

To Delligatti's delight, the product was "an immediate success," he said, adding that the recipe has not really changed in the 40 years since he sold the first Big Mac in Uniontown, Pennsylvania.

"The first day we just used the regular bun, we didn't have any center (bread) slice," Delligatti said. "Making it that way made it very sloppy. The next day we put the center slice in, and today it looks the same."

When Delligatti created the Big Mac in 1967, it cost 45 cents and McDonald's had just 1,000 restaurants. Today, the Big Mac sells for $2.69 at the Delligatti family's 18 McDonald's restaurants in Western Pennsylvania, and the world's largest restaurant chain has more than 31,000 outlets.

Along the way, the Big Mac's ubiquity has come to mirror that of the Golden Arches itself. It is even used to track the value of foreign currencies against the U.S. dollar in an annual "Big Mac Index" published by "The Economist" magazine.

Even after all that, however, Delligatti said he never received much from McDonald's for creating the Big Mac.

"All I got for the Big Mac was a plaque," he said, adding that he prefers eating the chain's Hotcakes and Sausage, another menu item for which he is responsible.

This week, however, Delligatti's role as the creator of the Big Mac will be in the lime light as a Big Mac Museum is opened inside one of the Delligatti family's McDonald's restaurants in North Huntingdon, Pennsylvania.

Not only will displays hold examples of the sandwich's original packaging and other Big Mac collectibles, but the restaurant will also house a bronze bust of the creator.

Delligatti is still active in the business he started in 1956 after learning about McDonald's during a trip to the National Restaurant Association trade show in Chicago.

Next month he will celebrate his 50th year as a McDonald's franchisee. The octogenarian still visits the office daily, and his son, Mike, who is also part of the business, said his father is still the boss.

"I just like to be involved with doing something," said the elder Delligatti. "I'm 89 years old, and I just would feel awful if suddenly I wasn't able to do that."

In recent years worries over the increasing rate of obesity have seen the Big Mac pilloried as an internationally recognizable symbol of junk food.

Times have been leaner since the millennium with McDonald's posting its first ever quarterly loss in 2002 and being forced to warn customers over the ingredients of its menu items in some countries.

In 2004 documentary maker Morgan Spurlock's iconoclastic movie Super Size Me introduced the world to the dangers of an all-McDonald's diet.

Yet the Big Mac remains a potent symbol of American food and ever-popular with youngsters.

Today, approximately 550 million Big Mac are sold each year in the United States alone.