Before the discovery of insulin, a diabetes patient must face an unavoidable death sentence. The discovery of insulin is a milestone in medical science, and it is really a revolutionary work for the welfare of the diabetes patients. In parallel it creates controversies and disputes among scholars; and disappointments, failures, and hopes in the way of discovery. The leading work to the discovery of insulin has been started in 1921 by the Canadian medical scientist and physician Frederick Grant Banting, who had no research experience, no publications, and not even a doctorate degree. He has started research through the supervision of Professor John James Richard Macleod; with two lab assistants of the bachelor degree students named Charles Herbert Best, and Edward Clark Noble, and ten dogs as experimental devices. The first applications of insulin in human body became possible in 11 January 1922 on Leonard Thompson, a 14-year-old boy who was suffering from diabetes mellitus. This study tries to discuss the aspects of discovery of insulin and the further continuous development of it for the welfare of the diabetes patients.