According to Wikipedia ” Plato was a Greek philosopher born in Athens during the Classical period in Ancient Greece.” He made an allegory called “Allegory of the Cave.” I will write about this and philosopher kings. 

According to Philosophyzer, “The ‘Allegory Of The Cave’ is a theory put forward by Plato, concerning human perception. Plato claimed that knowledge gained through the senses is no more than opinion and that, in order to have real knowledge, we must gain it through philosophical reasoning.” 

A king is someone who rules and most of them are hungry for power, so a philosopher king must be a person who is hungry for wisdom. And that is what Plato was.