as the club section—separating the two patties. The chain also popularized the drive-in restaurant format, taken and simplified by McDonald's type fast food operators. By the 1960s, Big Boy had expanded throughout the United States and Canada. Despite the benefits it provided to Wian, the chain was sold along with the rights to their signature Big Boy hamburger to the Marriott Corporation in 1967. This same year McDonald's franchisee Jim Delligatti, created an imitation of the Big Boy — the Big Mac. An example of the many McDonald's and White Castle imitators is Kewpee Hamburgers, a fast-food chain founded in 1923 in Flint, Michigan, by Samuel V. Blair as "Kewpee Hotel Hamburgs." As with the invention of the hamburger, the exact origins of the cheeseburger are unknown. Several chefs claim to have been the first to add a slice of cheese to a hamburger. Lionel Sternberger of Rite Spot in Pasadena, California, takes credit for the cheeseburger, claiming that he invented it between 1924 and 1926. A description from a 1928 menu from the O'Dell Restaurant in Los Angeles reveals that it was serving burgers with slices of cheese at the time. Luis Ballast, owner of the Humpty Dumpty drive-in restaurant in Denver, Colorado, made an attempt to create a cheeseburger with a registered trademark known as a "yellowburger" in 1935. J.C. Reynolds, the operator of a bar in Southern California from 1932 to 1984, popularized a pimento burger. Processed cheese, the type of cheese most used in cheeseburgers, was invented in 1911 by Walter Gerber of Thun, Switzerland, although the first U.S. patent awarded for it was given to James L. Kraft in 1916. Kraft Foods went on to create the first commercial version of sliced processed cheese, which was first introduced to the market in 1950.After World War II, a number of hamburger restaurants known as InstaBurger King (later Burger King) began emerging, the first of which was opened on December 4, 1954, in a suburb of Miami, Florida. It was established by James McLamore and David Edgerton, both of whom were students at the Cornell University School of Hotel Administration. McLamore had visited the original McDonald's in San Bernardino, California, when it was still owned by the McDonald brothers, and saw the potential that existed for the mass production of hamburgers. He was so inspired by this visit that he decided to create a similar burger chain