In the late 19th century, Dr. John Harvey Kellogg was the superintendent of Michigan's Battle Creek Sanitarium, a world-famous medical spa and grand hotel. He and his brother, W.K. (Will Keith) Kellogg, were also Seventh-day Adventists who believed in vegetarianism. The two were searching for wholesome foods to feed their clients, and especially ones that encouraged a healthy digestive system, as Dr. Kellogg saw a lot of patients with intestinal distress.
Although exact details of the cereal's invention remain disputed, we do know this: One day a batch of wheat-based cereal dough was left out and fermented. Rather than throw it away, the brothers sent it through rollers, hoping to make long sheets of dough. These sheets produced perfect flakes, which they toasted and served to their clients. The toasted flakes were a big hit, so the brothers patented them under the name Granose.
Over the years, W.K. experimented with other grains for use in the cereal, settling on corn, which produced crispier flakes. Eventually W.K. bought the rights to the cereal recipe and, in 1906, founded the Battle Creek Toasted Corn Flake Company, which began producing Kellogg's Corn Flakes.
When W.K.'s company became wildly successful, John got jealous and began making his own competing cereal. The two ended up suing one another. W.K. won in the end, but the brothers remained estranged until their deaths.