In 1951, Robert O. Peterson, the owner of a chain of successful local restaurants, developed a drive-through restaurant called Jack in the Box. Located primarily in California, Texas and Arizona, Jack in the Box restaurants featured a smiling clown named (What else?) Jack, who greeted motorists ordering through a two-way speaker device encased inside Jack's head.
During the early years, Jack in the Box business operations were conducted under various names and structures, including Foodmaker, Inc. In 1968, Jack in the Box was bought by the Ralston Purina Company as a wholly-owned subsidiary. Jack in the Box's management performed a leveraged buyout in 1985, and the company went public two years later. They changed their offical name in October 1999 from Foodmaker Inc. the Jack in the Box Inc.
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This is pretty much an edited version of the Jack in the Box website's own history.
Sources
http://jackinthebox.com