Ivan Pavlov was a Russian physiologist best known for his research on classical conditioning. He conducted experiments with dogs, where he discovered that they could learn to associate a neutral stimulus, like a bell, with food. Over time, the dogs would salivate at the sound of the bell, even when no food was presented. Pavlov's work laid the foundation for behaviorism, a major psychological theory. His findings demonstrated how behaviors can be learned through association, influencing various fields, including psychology, education, and animal training. His research remains significant in understanding how learning occurs.