In Plato's Republic, a ruler who combines political power with philosophical knowledge of the good; Plato argued that cities will not be free of evils until philosophers rule or rulers become philosophers.
In more detail
The philosopher-rulers of the Republic are selected and trained through a long education in mathematics and dialectic, live without private property or private families, and rule out of duty rather than ambition. The idea is the classic source of arguments for rule by the knowledgeable. Critics from Aristotle to Karl Popper and Robert Dahl object that no reliable method exists to identify such rulers or to keep them accountable, and that political judgement is not a matter of expertise alone. Modern debates on epistocracy, technocracy and AI-assisted government often revisit the same questions.