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.
Dihydrotestosterone
DHT was first synthesized by Adolf Butenandt and his colleagues in 1935. It was prepared via hydrogenation of testosterone, which had been discovered earlier that year. DHT was introduced for medical use as an AAS in 1953, and was noted to be more potent than testosterone but with reduced androgenicity. It was not elucidated to be an endogenous substance until 1956, when it was shown to be formed from testosterone in rat liver homogenates. In addition, the biological importance of DHT was not realized until the early 1960s, when it was found to be produced by 5α-reductase from circulating testosterone in target tissues like the prostate gland and seminal vesicles and was found to be more potent than testosterone in bioassays. The biological functions of DHT in humans became much more clearly defined upon the discovery and characterization of 5α-reductase type II deficiency in 1974. DHT was the last major sex hormone, the others being testosterone, estradiol, and progesterone, to be discovered, and is unique in that it is the only major sex hormone that functions principally as an intracrine and paracrine hormone rather than as an endocrine hormone.