Answer: Ivan Pavlov
Due to his experiments, he influenced other scientists. The experiment that he is most known is: Pavlov's dogs.
Pavlov fed
dogs and was looking at salivation in response to the food. At a certain
point, whenever he entered the
room, the dog would start to salivate even when he was not bringing them
food. This it is an unconditioned response to an unconditioned
stimulus.