If you describe someone as a disciplinarian, you mean that they believe in making people obey strict rules of behaviour and in punishing severely anyone who disobeys. He has a reputation for being a strict disciplinarian. = authoritarian. someone who believes people should obey orders and rules, and who makes them do this
One who disciplines; one who excels in training, especially with training, especially with regard to order and obedience; one who enforces rigid discipline; a stickler for the observance of rules and methods of training; as, he is a better disciplinarian than scholar