Final answer:
John B. Watson and B. F. Skinner are the two key early proponents in the behavioral approach, with Watson being the founder of behaviorism and Skinner further developing the theory.
Step-by-step explanation:
Two key early proponents in the behavioral approach were John B. Watson and B. F. Skinner. Behaviorism is a school of thought in psychology that emphasizes the importance of observable behaviors over internal mental processes. Watson is credited as the father of behaviorism and was a major advocate for focusing psychology on observable behavior. Skinner continued to advance behaviorism by studying how behavior is affected by its consequences, introducing concepts like reinforcement and punishment.