fundamentalist
This term carries a strong connotation of rigidity and uncompromising adherence to a set of core tenets. While it can be used neutrally to describe a strict follower of a doctrine, it often implies a rejection of modernity, nuance, or compromise, frequently appearing in political or religious discourse to describe an extremist stance. In a non-religious context, the word describes someone who insists on a literal or absolute application of a specific ideology or set of rules, regardless of changing circumstances or practical contradictions.
Meanings
A person who adheres strictly to the basic principles of a religion or ideology, often rejecting modern interpretations or compromises.
"The group was led by a religious fundamentalist who demanded a return to the original scriptures."