John James Rickard Macleod (6 September 1876 – 16 March 1935) was a Scottish physician and physiologist. He was noted as one of the co-discoverers of insulin and given the Nobel Medal for this discovery. Macleod's main work was on carbohydrate metabolism and his efforts with Frederick Banting and Charles Best in the discovery of insulin used to treat diabetes. For this Banting and Macleod were jointly awarded the Nobel Prize for Medicine in 1923. Macleod was awarded half of the Nobel Prize for the discovery of insulin in 1921 which he shared with James B Collip.