McDonald’s is celebrating the 50th anniversary of its world famous Big Mac.

The Big Mac has been one of the most popular and best-selling items in the company’s history. It is known for being bigger than a usual hamburger, with two pieces of meat separated by an extra piece of bread in the middle. It is also made with special sauce and toppings.

As part of a memorable advertising campaign in the 1970s, the Big Mac’s ingredients were sung to music to help keep them in people’s minds.

Two all-beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun. The Big Mac generally contains the same ingredients in McDonald’s restaurants around the world.

The Big Mac was invented in 1967 by Jim Delligatti, the local operator of several McDonald’s in the American state of Pennsylvania. He urged the company to let him sell the special hamburger at all the restaurants that he ran.

Delligatti died in 2016 at the age of 98. In a 2007 interview with Reuters, he said it took a long time to persuade McDonald’s that the Big Mac was a good idea. “I felt that we needed a big sandwich,” he said. “But you couldn’t do anything unless they gave you permission.”

McDonald’s finally agreed to let Delligati sell the sandwich at one of his McDonald’s restaurants. The company required him to use the same bun that other McDonald’s burgers were made with.

For that reason, Delligati said, it did not sell well at first. When he changed to a bigger bun -- topped with sesame seeds -- sales of the sandwich increased by more than 12 percent.

After similar results at other stores, McDonald’s decided to add the Big Mac to all its restaurants in 1968. The Big Mac then grew to become an international food star. The Economist magazine has even used the price of the Big Mac to measure the purchasing power of different international currencies.

To celebrate the Big Mac’s lasting popularity, McDonald’s is launching a series of collectible MacCoins. They will be available starting August 2 around the world. The company chose that day because August 2 would have been Jim Delligatti’s 100th birthday.

The coins can be shared or collected. People can also trade them in for a free Big Mac. McDonald’s plans to give away more than 6.2 million MacCoins in more than 50 nations. The coins come in five designs, each representing a different 10-year period with the Big Mac.