What PC class should a well-designed ruler have?

[Berenger]

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.

Running around on a battlefield to try and save the lives of a handful wounded soldiers, acting as a court clerk and spamming Zone of Truth until the last one in a bunch of suspect cattle thieves fails his will save, healing two people per day from disease and blessing farmland 0,7 acres at a time is actually kind of nice if you are responsible for the welfare of some idyllic village.

Lord Angmar is supposed to govern a whole province of an empire. If we take something like the Roman Empire as an example, we are talking about a domain roughly the size of England with anywhere from a few hundred thousand to a few million inhabitants. If the ruler of a political entity on this scale develops a habit of wasting his time getting involved in that kind of micro-management, all is lost.

This guy should concentrate on doing his actual job, which is making political and military decisions that affect the province as a whole. This absolutely includes fostering and maintaining a good relationship with religious cults whose members can in turn provide above services to the population.