rigorist

/ˈrɪɡərɪst/
noun
  1. A person who insists on strict adherence to rules, principles, or standards, especially in matters of morality or religion.
    • The coach was known as a rigorist, requiring players to practice the same drill for hours until it was perfect.
    • As a religious rigorist, she believed that even small deviations from tradition were unacceptable.
    • The school principal was a rigorist who demanded that every student follow the dress code exactly.