Ivan Pavlov
Russian physiologist, 1849-1936
"Ivan Petrovich Pavlov was a Russian physiologist known primarily for his work in classical conditioning. Pavlov's dog is named in his honour. Pavlov had learned that when a buzzer or metronome was sounded in subsequent time with food being presented to the dog in consecutive sequences, the dog would come to associate the sound with the presentation of the food and salivate upon the presentation of that stimulus. Pavlov’s ""The Work of the Digestive Glands"" (1897) served as a base for broad research on the digestive system. His experiments earned him the 1904 Nobel Prize in Physiology and Medicine."
Source: Wikipedia