Complex sentence: Ralston Purina tried further to mature the restaurant's image, renaming it "Monterey Jack's" in late 1985, a disastrous move; the Jack in the Box name was restored in early 1986.
Split into simpler sentences: Ralston Purina tried further to mature the restaurant's image, renaming it "Monterey Jack's" in late 1985. The name change proved to be a disaster, and the Jack in the Box name was restored in early 1986.