McDonald's introduced the Quarter Pounder in 1971. It was created by Al Bernardin, a McDonald's franchise owner and former product-development executive, at his restaurants in Fremont, California.
The burger was named for its uncooked beef patty, which originally weighed approximately one quarter of a pound, or four ounces. Bernardin introduced it locally with the slogan “Today Fremont, tomorrow the world,” and its popularity led McDonald's to add it to the national U.S. menu in 1973.
The classic Quarter Pounder with Cheese is served with toppings such as pickles, onions, ketchup, mustard, and cheese, although exact recipes vary by country. In markets that do not commonly use pounds, the sandwich may have another name, including Royal or McRoyale.
A frequent confusion is between the product's creation date and its nationwide rollout. The Quarter Pounder began in 1971 at Bernardin's Fremont restaurants; McDonald's expanded it across the United States in 1973. The question asks when it was introduced, so 1971 is the canonical answer.