The McDonald brothers met Ray Kroc when he sold them milkshake machines.

Kroc returned home after participating in World War I and started playing the piano. However, he disliked the long hours, so after getting married, he began working in sales. He worked for the Lily Tulip Cup Company selling paper cups for 17 years. Ray Kroc's occupation as a traveling milkshake machine salesman when he met the McDonald brothers, who had bought eight milkshake machines, is an interesting fact about Ray Kroc. He was amazed by the aggressive sales tactics he used, and they were impressed by how quickly and cheaply the brothers were able to serve customers by keeping their menu simple—just burgers, fries, and shakes. In 1954, he signed on with the business as a franchise agent in exchange for a meager cut of the revenues.

He was a salesman for Multimixer milkshake equipment at the time. When the McDonald Brothers purchased eight machines at a time when sales were declining, Ray's focus turned to them. Following their meeting with the brothers, the three of them recognized promise in one another, leading to a commercial collaboration between Ray Kroc and the McDonald Brothers.

By the time the brothers met Ray, they had already opened eight other locations and licensed 20 additional franchises. Only when they got to know Rey and began working with him did McDonald's business start to really take off.