Paul Johannes Tillich was a renowned theologian and philosopher whose work focused on the relationship between religion and culture. Synonyms for Tillich include "Christian existentialist," "neo-orthodox theologian," and "theologian of culture." Tillich's ideas were influential in the mid-20th century, particularly his concept of the "ground of being," which he believed was the ultimate reality behind all existence. Other synonyms for Tillich include "systematic theologian," "Protestant theologian," and "theologian of hope." His work explored the nature of faith and doubt, and offered new insights into the meaning of human existence in a changing world.