Who believed in "unity of production" which led to the development of the director?

The person behind the so called "unity of production" was Wagner.

He demands sought to filter all stage expressions through a single artistic consciousness. To realize his goal, he built a new kind of theater building and it was the first in the West to do away with the box, the pit, and the gallery arrangement in favor of a democratic configuration. Wagner's contribution to the development of the director came from his strong demand for "unity of production" which meant everything has been filtered through a single consciousness to achieve a unified artistic effect.