What is a philosopher and why is the philosopher the best ruler?
A part of Plato's Republic deals with the question of who would make the ideal ruler. In the Republic, the philosopher is the person who can see past the appearance of things and get at their Form, the ideal that each of the individual instances reflects/participates in. They have access to the "truth" in a way that ordinary people do not. Individuals may have access to small parts of the truth, but they do not see the whole.
"Until philosophers are kings, or the kings and princes of this world have the spirit and power of philosophy, and political greatness and wisdom meet in one, and those commoner natures who pursue either to the exclusion of the other are compelled to stand aside, cities will never have rest from their evils - no, nor the human race, as I believe - and then only will this our State have a possibility of life and behold the light of day." ~ Plato, The Republic, Book V, 473-C
The philosophers then undertake an extensive program of training in all the skills that will be needed to rule. Unlike our present system in America, which demands only that you be born here, but of a certain age, and have enough money to run an effective "campaign," Plato's rulers have nothing to gain as a result of their rule, and have the skills they need to understand why things happen and what they are able to do to deal with them.
Sounds like a plan to me.
A philosopher is the one who has mastered the art of life .For example,they clearly know when to use head and when to use heart. They use their head when they have to command themselves, but in the circumstances when they have to command others, they leave the job to their hearts.They can ,no doubt,make an ideal ruler,for they know how to renounce and enjoy.