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.
James Francis Tait
James Francis Tait was an English physicist and endocrinologist. He worked with his wife, Sylvia Agnes Sophia Tait from 1948 until her death in 2003, a partnership described by the Oxford Dictionary of National Biography as "one of the most successful examples of husband-wife collaboration." Together, they discovered and identified the hormone aldosterone.