Angels & Demons
In a word: Rangers.
Unless otherwise specified by the DM, all Rangers are sworn to serve the King of the realm and operate under his authority rather than any feudal lord who’s lands they inhabit. They are an ancient guild of highly trained outdoorsmen (and women) who through their complex web of communications keep the King informed of all the goings on within his extensive realms.
As operatives embodying the King himself, the King’s Men have considerable authority. However, while their authority is technically wide-reaching they are not law enforcement agents, spies, or assassins. They function primarily as a group dedicated to keeping roads open, the wilderness explored, and bandits at bay or running in fear. Secondarily they are an unobtrusive intelligence gathering resource for the King and keep him informed as to the myriad of goings on throughout his kingdoms.
It is illegal for anyone except the King to detain, imprison, or impede a King’s Man for any reason. They are under no obligation to explain their comings and goings to anyone other than the king as well, although this has been tested by many rulers throughout the centuries. Many local rulers and judiciaries see the King’s Men as helpful non-partisan allies who support civilization at large and their ruler, but there is always a few who are jealous of the carte blanche they are afforded and seek to trap them politically or otherwise, almost always to the extreme displeasure of the King.
Their origins are lost to antiquity but there has never been a King in the history of the realm who did not rely upon his King’s Men to keep him appraised and informed about the state of the roads, banditry and the movement of troops, commerce, and people. The Cartography room within the royal palace is under the control of the King’s Men and is the largest collection of maps in the known world. King’s Men are some of the greatest adventurers and explorers ever and they are able to write down nearly every place they have been to help future generations.
The King’s Men do not take sides but will fight for the King in the event of an uprising and will inform the King of any large movements of troops and they keep explicit track of troop counts within the realms they are assigned to. In fact, any group of nobles contemplating a revolt or any cast off relative wanting to gather an army to dethrone the sitting King has more to fear from the King’s Men than just about any other group within the realm. As such, the King’s Men are one of the greatest stabilizing forces in the kingdom and have contributed directly to many millenia free from civil wars.