Ivan Pavlov is known for the theory of classical conditioning. He was a Russian physiologist best known for his research on the digestive systems of dogs, which led to the discovery of conditioned reflexes. In his famous experiments, Pavlov demonstrated how dogs would salivate in response to a neutral stimulus, such as a bell, when it was repeatedly presented alongside food. This process showed that animals could learn to associate different stimuli, leading to automatic responses. Pavlov’s work laid the foundations for behavioral psychology and has had a profound impact on understanding learning, behavior modification, and conditioning processes in both animals and humans.