[Gumby Bush]

In the D&D campaign I am currently playing in, my Knowledge Cleric is out to establish a theocracy using mind control spells... Geas is useful for this, along with Suggestion. Thaumaturgy, Enhance Charisma, and Command supplement it nicely. Further, Zone of Truth can be used to check for loyalty, and Sending helps long-range communication. He will also use Continual Light to provide lights in the cities (he's already started in the one city where he already has power). I expect to follow this campaign with a GURPS campaign where he is a villain running the theocracy with mind control and patronage of the arts and sciences (and thus getting the bards to like him, providing free propaganda). He gains access to the last of these spells at level 9. The use of Geas on underlings seems like it would be a common practice among clerics in many realistic settings (and seen almost akin to signing non-disclosure and non-compete clauses today).

The setting has magical ability be relatively rare and divine intervention almost solely through clerics and paladins, of which there are not many, which helps one to gain immense power--there aren't many around who can counteract his actions.

50 years later, however, the cleric will have trained others, and one of the other characters will have inducted the local goblins into his cult to an old one... Assuming none of these gets killed off before the campaign ends.