What PC class should a well-designed ruler have?

[Yahzi Coyote]

So what is that class?

Cleric is always the best for social control.

Cure Minor Wounds - stops people from bleeding out. This is better than modern medicine can do.
Zone of Truth - pretty much ends all crime.
Remove Disease/Blindness/Deafness - stop plagues before they start, and again, better than the Mayo clinic.
Plant Growth (with Plant domain) - equal to modern fertilizer, and a single 5th level cleric can support a small city. This single-handedly rings in the Industrial Revolution, because your society has so much food it can afford to invest in craftsmen.

The ability to heal soldiers, save birthing mothers, and cure children makes for very loyal henchman. And that's at 5th level, before you can raise the people who die serving you.