Ivan Pavlov is credited with defining the theory of classical conditioning in psychology. His foundational research began with experiments on dogs, where he discovered that dogs would salivate upon hearing a bell associated with food. This conditioned response demonstrated how associative learning occurs when a neutral stimulus becomes linked to an unconditioned stimulus, leading to a learned behavior. Pavlov's work laid the groundwork for behavioral psychology and influenced later researchers, including John B. Watson and B.F. Skinner, who further explored conditioning and behavior. Pavlov’s findings remain critical in understanding learning processes across various disciplines, including psychology and education.