John Campbell is a resident of Mr. Pleasant, Ohio, who had moved to the town from New York, New York. He is a professor at the college there, and had met Professor Hubert Windlenot. He is also the father of Merrick Campbell.
It is obvious that he cares about his son, and wants what is best for him. That was part of his reasoning taking the teaching job in Mt. Pleasant. He liked Beth Ann Nelson for his son's company and he used to invite her for dinner; apparently he knew that Beth liked his son and hoped that they'd get along. He may have suspected that his son had gone up to the museum when the two had disappeared, knowing his son’s fascination with the man.