The Big Mac was invented by Jim Delligatti, one of the earliest McDonald's franchisees, who operated in the Pittsburgh area. Delligatti's McDonald's kitchen in the Ross Township of suburban Pittsburg was the birthplace of the Big Mac in 1967.
The sandwich had 2 names before McDonald's settled on Big Mac. First, it was called 'Aristocrat,' which apparently was too difficult for costumers to pronounce. The second name was 'Blue Ribbon Burger,' but that failed to spark any meaningful sales.
Finally, Esther Glickstein Rose, a 21-year-old Advertising Secretary at MacDonald's Corporate HQ in the suburbs of Chicago coined the term Big Mac. That name stuck and it became the world's most famous fast food sandwich.