The correct answer is: "a ruler whose associates make all the decisions for him".
This type of ruler holds an official title (for example, president or minister), but actually he is not performing the decision-making, there is a person or a team behind him who does so, therefore he exercises little de facto power.
This scenario was common with medieval kings, who were the legitimate owners of the title but many times other men were actually ruling on their behalf, as they did not have the capacity to do so or they were not interested in governing.