What is the opposite of a Unitarian?

Answer 1

Unitarians (and Unitarian Universalists) are primarily characterized by an openness to new ideas, to freedom belief, and to the use of reason in religion. In that sense, the opposite of a Unitarian would be a religious person who is closed to new ideas, insists on uniformity in religion, and considers reason to be irrelevant in religion.

A religious fundamentalist or religious literalist would thus be a good candidate for an opposite to a Unitarian.