Step 1: Understanding the Concept: 
The question asks to identify the founder of Behaviour Therapy. Behaviour therapy is a broad term for psychotherapies that treat mental health disorders by focusing on changing maladaptive behaviors. It is rooted in the principles of behaviorism. 
Step 2: Detailed Explanation: 
While Behaviour Therapy has many contributors (like Ivan Pavlov, John B. Watson, and Joseph Wolpe), B.F. Skinner's work on operant conditioning is a fundamental pillar of the field. His principles of reinforcement, punishment, and shaping form the basis of many behavioral techniques, especially Applied Behavior Analysis (ABA). 
(A) Clark Hull was an influential behaviorist, but his work was more theoretical and less directly translated into therapeutic techniques than Skinner's. 
(C) Sigmund Freud founded psychoanalysis, which is fundamentally different from and often contrasted with behavior therapy. 
Given the choices, B.F. Skinner is the most appropriate answer as his foundational work in operant conditioning is central to the development and practice of behavior therapy. 
Step 3: Final Answer: 
B.F. Skinner is considered a key founder and influential figure in the development of behaviorism and its application in Behaviour Therapy.