The influential psychologist who founded the field of behaviorism is John B. Watson. He proposed that psychology should focus on observable behaviors rather than internal mental states. Watson's famous experiment with Little Albert demonstrated how emotional responses could be conditioned, highlighting the role of the environment in shaping behavior. His advocacy for a scientific approach to psychology revolutionized the field and influenced subsequent psychologists, including B.F. Skinner. Watson's legacy endures in behavioral therapy and education, emphasizing the importance of external stimuli in understanding human actions and responses.