Secretin
Secretin was the first hormone to be identified. In 1902, William Bayliss and Ernest Starling were studying how the nervous system controls the process of digestion. It was known that the pancreas secreted digestive juices in response to the passage of food (chyme) through the pyloric sphincter into the duodenum. They discovered (by cutting all the nerves to the pancreas in their experimental animals) that this process was not, in fact, governed by the nervous system. They determined that a substance secreted by the intestinal lining stimulates the pancreas after being transported via the bloodstream. They named this intestinal secretion "secretin". Secretin was the first such "chemical messenger" identified. This type of substance is now called a hormone, a term coined by Bayliss in 1905.
Arthur Riggs (geneticist)
Riggs and Itakura collaborated with Herbert Boyer at Genentech, and used recombinant DNA technology to become the first to produce a human protein in E. coli. Following the advice of Riggs and Itakura, the group successfully produced the hormone Somatostatin in 1977 as a proof of concept before they attempted to work with the more complicated insulin molecule. They were able to link somatostatin to a larger protein, beta-galactosidase, produce it in E. coli, isolate it, and then separate the somatostatin from the galactosidase. Somatostatin was the first mammalian hormone to be produced in a bacterium.