The correct order, from highest to the lowest is the following. 1) monarchs, 2) clergy, 3) nobles, 4) knights, 5) merchants, 6) artisans, 7) serfs.
The most powerful man in Medieval times was the King. He amassed great power and territories due to his many conquests. The clergy was the members of the church, influential priests that supported the king and somewhat controlled the lower classes by the element of faith. Nobles were wealthy men that owned property and supported the King in a convenient relationship. Knights were brave men at the loyal service of the Nobles and the King. The lower classes in Medieval times were merchants, peasants, and serfs, that worked for the King or the Nobles. Their living conditions were so different than the other classes and worked hard to make a living.