Final answer:
Plato believed that a philosopher-king would be the ideal ruler to ensure order and justice in society, as they possess the wisdom and virtue necessary for governance.
Step-by-step explanation:
According to Plato's The Republic, the type of person he believed would ensure the most order and justice in a society as the ruler is a philosopher-king. Plato's ideal system of government emphasized the rule by philosophers, as they were deemed capable of accessing the immaterial realm of forms and having the clearest understanding of virtues like wisdom, justice, and courage. This concept of a philosopher-king is central to Plato's political philosophy, where the ruler would be free from temptations to corruption and understand what is best for the community. In Plato's just city, individuals would occupy roles they are best suited for, with the philosopher-king being the natural ruler, trained from infancy to serve the needs of society with wisdom and virtue.