Ivan Pavlov was a Russian physiologist born in 1849 who is known for his work on classical conditioning. He discovered that dogs could learn to associate stimuli through repeated pairings, such as salivating when hearing a bell that was paired with food. Pavlov received the Nobel Prize in 1904 for his research on the digestive system, which led him to discover conditioned reflexes. He spent his career researching conditioning at the Institute of Experimental Medicine in St. Petersburg until his death in 1936.