Orville Redenbacher was a real person, and so was Colonel Sanders, although he wasn't really a colonel. Dave Thomas, who founded the Wendy's chain, had a real daughter named Wendy. Jack Daniel was real, and so was Johnnie Walker.

Betty Crocker was fake. Duncan Hines was real; he was probably the first restaurant reviewer, but I don't think he ever founded or owned any food-producing business. He just licensed the use of his name.

Kellogg, Post, and Graham (as in Graham cracker) were all real people who started as health-food promoters.

A novel and a movie The Road to Wellville were made about John Harvey Kellogg, starring Anthony Hopkins as Kellogg.