The Temple of Celestial Revolution houses an order of Templar that overthrow stable governments. When their astrologers tell them a government has ruled long enough to build up a toxic layer of secrets, they use a wide variety of tactics to overthrow that government--then they withdraw. They read the stars, waiting until the time is right to slay all the dragons and wizards to cleanse the world of magic. The Templar worship the goddess of the moon, and that makes them dangerous lunatics.
This system-neutral resource has the framework for the Templar, sample NPCs, suggestions for varying difficulty, a waystation, and suggestions for working all this in to your current game.