The thinker who does NOT belong among the behaviorists is Sigmund Freud.
Freud is known for founding psychoanalysis, which emphasizes the importance of unconscious processes and early life experiences, rather than focusing solely on observable behaviors, which is the main focus of behaviorism. The other thinkers listed—Ivan Pavlov, J.B. Watson, and B.F. Skinner—are all major figures in the behaviorist movement.