He was a Russian physiologist who studied the digestive system of dogs. During his research, he noticed that dogs would salivate before they were even given food, simply at the sight of their feeder. This led him to conduct his famous experiments, where he would ring a bell just before giving the dogs food. Eventually, the dogs learned to associate the bell with food and would salivate just at the sound of the bell, even without the presence of food.
This discovery led to the concept of classical conditioning, a fundamental principle of learning where a neutral stimulus (the bell) is paired with an unconditioned stimulus (food) to create a conditioned response (salivation).