Glucagon is produced in the alpha cells and works to increase blood sugar levels. Insulin is from the beta cells.
Most folks assume that the hormone called insulin is at the heart of diabetes: either there’s not enough of it or it’s not working right.
But thats’s not the only possible mechanism for diabetes. I’ve written several times here about the glucagon-centric theory of diabetes, which is most closely associated with Roger Unger, M.D. If you’re interested in a scientific review article on glucagon and type 2 diabetes, here’s one:
Reference: Xiao C. Li and Jia L. Zhuo. Current Insights and New Perspectives on the Roles of Hyperglucagonemia in Non Insulin-dependent Type 2 Diabetes. Current Hypertension Reports. Oct 2013; 15(5): 10.1007/s11906-013-0383-y. doi: 10.1007/s11906-013-0383-y
Front cover of book
Diabetic Mediterranean Diet 
Unger’s experiments are elegant but the conclusion is not so different from what we teach students. Insulin is still, more or less, the master hormone but it acts in an indirect way. It reduces blood glucose by inhibiting the effect of glucagon. My youtube shows this: https://www.facebook.com/richard.feinman.7/posts/957009657717305
Many systems in biology are controlled negatively. For example, the retina is a dark receptor. Light turns off activity. More generally, protein/enzyme systems evolve to reduce activity. An enzyme that has evolved for high activity needs to be kept under control to function in a biological system. In essence the glucose producing system seems to be biased to be in the ‘on’ state and insulin dials things back.
Thanks for that insight, Dr. Feinman.