Old Grand-Dad was a real person, a distiller named Basil Hayden who made his name by distilling a bourbon whiskey made with a higher percentage of rye. Basil Hayden passed along the art of distilling to his son and then, in turn, to his grandson. It was the third generation distiller, Colonel R.B. Hayden, who honored his grandfather by naming his justly famed whiskey "Old Grand-Dad."
During Prohibition, this bourbon was produced by a pharmaceutical company, the American Medicinal Sprits Co., and was one of the few distilled spirits permitted to be prescribed as medicine. It was a popular time to be sick.
Today, Old Grand-Dad is one of the top 10 best-selling bourbons. It is specifically formulated with more rye for a lighter, spicier flavor along with fruity and oaky notes. (from the distiller)