The cereal James Caleb Jackson introduced in 1863 was Granula.
Jackson, a physician and health reformer, developed Granula at the Jackson Sanatorium in Dansville, New York. He made the cereal from graham flour, baking it into a dense product and breaking it into pieces. Because the pieces were hard, consumers were advised to soak them before eating.
Granula is widely credited as the first ready-to-eat breakfast cereal, although its preparation differed from modern cereals. It was not eaten dry straight from a box in the way many contemporary cereals are. The product also became involved in an early naming dispute: John Harvey Kellogg later sold a similar cereal called Granola, and Jackson’s company objected to the similarity.
Granula is often mixed up with granola, the later cereal name that became common after the legal dispute. Grape-Nuts, Shredded Wheat, and Wheaties were introduced decades afterward, so they cannot be the 1863 product.