In his masterpiece, the Republic, Plato argues that the just state is ruled by those who know the Good, and at the top is the philosopher-king, a man born and literally raised to rule.
Although it may be tempting to regard Marcus Aurelius (121-80 AD) as a philosopher king, this would be a mistake. Marcus was a philosophically inclined Roman emperor, but not a philosopher-king in Plato’s sense. Among other things, he failed to undertake the rigorous curriculum required by Plato, and anyway, the philosophy that Marcus espouses, while platonic in places, is clearly generally Stoic in nature. However, it would also be a mistake to neglect Marcus, to take him for a second-rate thinker who just happens to be an emperor. We have, in his writings, nothing less than a sort of distillation of Stoic philosophy that is filtered through the practical demands of someone in possession of monumental political power.
His journey to power was unusual. Marcus was adopted and well brought up by his uncle, Emperor Antonius Pius (himself adopted by Emperor Hadrian). By all accounts Marcus was an excellent student of rhetoric, poetry, and law, but he seems to have taken an early and keen interest in philosophy, especially the writings of the Stoic Epictetus. At an early age, perhaps as young as 11, he began to dress simply and follow what he saw as the stern regimen of study, frugality, and self-sacrifice of a Stoic. Maybe he went too far, as there are reports that his health has suffered.