Original
I don't know who officially found diabtes to be a disease, but Canadian scientist Frederick Banting and medical student Charles H. Best discovered the hormone insulin in pancreatic extracts of dogs. On July 30, 1921, they injected the hormone into a diabetic dog and found that it effectively lowered the dog's blood glucose levels to normal. In medieval times, they called Diabetes the "Wasting Sickness" as the victims quite literally wasted away to nothing, because of the sudden weight loss and loss of appetite.