Final answer:
The theorist credited with developing the theory of systems is von Bertalanffy.
Step-by-step explanation:
The theorist credited with developing the theory of systems is d. von Bertalanffy. Ludwig von Bertalanffy was an Austrian biologist who proposed the concept of general systems theory. This theory emphasizes the interrelatedness and interconnectedness of various components within a system, and it has been widely influential in fields such as biology, psychology, and sociology.