McDonald's was founded in 1955 by Oak Park native Ray Kroc, who worked as a salesman of milk shake machines. In 1954, Kroc encountered the hamburger stand of the McDonald brothers in San Bernardino, California, which used Kroc's mixers. After convincing the McDonalds to name him their exclusive franchising agent, Kroc opened a restaurant in Des Plaines; it was the first McDonald's in the Chicago area. The chain grew at an extraordinary rate: there were 14 restaurants in 1957 and 100 by 1959. In 1961, when there were 250 restaurants in the chain, Kroc purchased the interest of the McDonald brothers for $2.7 million. By 1968, three years after it started to advertise on television, Kroc's company oversaw 1,000 McDonald's franchises. The remarkable growth continued during the 1970s, when McDonald's—now based in Oak Brook—added 500 new restaurants each year in locations around the world. With this rapid expansion, annual revenues passed $1 billion. The company had become one of the world's largest users of beef, potatoes, ketchup, and other foods; its distinctive golden arches had become a familiar part of the landscape. By the beginning of the century, there were about 25,000 McDonald's restaurants around the world, annual revenues stood at about $15 billion, and over 400,000 employees worked for the company, which had become a symbol of America around the world. In the Chicago area, the company employed about 6,000 people.