What do you call someone who is rigid?

Someone who is rigid can be called inflexible, stubborn, strict, uncompromising, obstinate, uptight, or set in their ways, depending on context. In personality terms, rigid person might be called disciplinarian if they enforce strict rules, perfectionist if they demand exactness, authoritarian if they demand obedience to rigid rules, or stickler if they insist on precise compliance. In psychology, rigid person might be described as having rigid personality traits, obsessive compulsive personality traits, or being inflexible and resistant to change. Colloquially, you might call rigid person uptight, stiff, or hard-nosed. If rigid refers to physical stiffness, you might call them stiff. So terms include inflexible person, strict person, stubborn person, uncompromising person, and obstinate person, all describing someone who does not adapt, does not bend rules, and insists on own way, often seen as difficult to work with because they resist new ideas and changes.