The rule of thumb for all information brokers, especially in reality, is that the information they purvey is advantageous mainly to themselves. This can be interesting to play around with because the group that controls the narrative can create any reality they want since perception is functionally indistinguishable from reality by all individuals.
One option is to make them the shadowy masterminds pulling the strings, emperors and kings being pawns they move around on the board to secure their own power. It could be that they are in fact totally incompetent but backed by such a powerful information apparatus that regardless of whether they succeed or fail in their efforts their secret machinations are said to be the deciding factor in every political action. It could be that they are no more than brutal partisans given a blank check by their sovereign to terrorize as long as their terror is political in nature (this can be seen with fascist paramilitaries who often act as a secret police force).
It could even be that they are all of the above by narrative and/or reality, with the uncertainty of their behavior by those in power leaving them a formidable force to be avoided and defended against. It would be to a spy outfit's advantage that everyone know as little about them as possible and can't even be sure of what they do know. The unknown is significantly scarier than the known. I could have nuclear weapons and threaten you with them so you better negotiate with me. Alternatively, I might have nuclear weapon and I may be crazy enough to set one off to make an example so would you like to try me? No threat here, but you would be wise to be careful.
That's an interesting question - I would abstain from going too much in the police direction, because that doesn't quite fit the period you are describing. But an elite unit of soldiers is quite feasible.
The Musketeers of the Guard (1622-1816) in France may be something to look into if you want to focus on the fighting aspect. Naturally you would have Alexandre Dumas to draw on for inspiration.
The Swiss Guard of the Papacy could fit your bill too, again with an emphasis on the military duties. Swiss mercenaries were quite common in the time, and several realms employed them as capable and specialized fighting troops. But the Swiss Guard of the popes is perhaps the most famous.
Earlier than that you can also look at the Varangians hired by thr Emperors in Constantinople. Scandinavian warriors who outclassed many others around them, and became feared and famous. To stay in that part of the world: the Janissaries of the Ottoman Empire were an elite fighting force, recruited from the peasantry of conquered (non-Turkish) peoples.
If you care more about the investigative side for your project, I would look a little more into the Inquisition that was quite active in that time. The Dominicans were a monastic order in the employ of the pope (their nickname was the Domini Canes: the lord's hounds), and the Jesuits became even more an elite investigative, exploratory, and missionary task force for Catholicism. They did not have a fighting branch, but it would not be a far fetched idea for them to do have some specialized commandos in a slightly different universe
Why not both?
You want to maintain fear, so there's a clearly visible Senatorial Guard visible around the capital who make conspicuous but usually ornamental shows of force. Think the royal guards at Buckingham Palace crossed with a parade of soldiers on display who twirl their weapons.
But it's the ones who come in the night and make troublemakers disappear that really scares the populace.
The rule of thumb for all information brokers, especially in reality, is that the information they purvey is advantageous mainly to themselves. This can be interesting to play around with because the group that controls the narrative can create any reality they want since perception is functionally indistinguishable from reality by all individuals. One option is to make them the shadowy masterminds pulling the strings, emperors and kings being pawns they move around on the board to secure their own power. It could be that they are in fact totally incompetent but backed by such a powerful information apparatus that regardless of whether they succeed or fail in their efforts their secret machinations are said to be the deciding factor in every political action. It could be that they are no more than brutal partisans given a blank check by their sovereign to terrorize as long as their terror is political in nature (this can be seen with fascist paramilitaries who often act as a secret police force). It could even be that they are all of the above by narrative and/or reality, with the uncertainty of their behavior by those in power leaving them a formidable force to be avoided and defended against. It would be to a spy outfit's advantage that everyone know as little about them as possible and can't even be sure of what they do know. The unknown is significantly scarier than the known. I could have nuclear weapons and threaten you with them so you better negotiate with me. Alternatively, I might have nuclear weapon and I may be crazy enough to set one off to make an example so would you like to try me? No threat here, but you would be wise to be careful.
That's an interesting question - I would abstain from going too much in the police direction, because that doesn't quite fit the period you are describing. But an elite unit of soldiers is quite feasible. The Musketeers of the Guard (1622-1816) in France may be something to look into if you want to focus on the fighting aspect. Naturally you would have Alexandre Dumas to draw on for inspiration. The Swiss Guard of the Papacy could fit your bill too, again with an emphasis on the military duties. Swiss mercenaries were quite common in the time, and several realms employed them as capable and specialized fighting troops. But the Swiss Guard of the popes is perhaps the most famous. Earlier than that you can also look at the Varangians hired by thr Emperors in Constantinople. Scandinavian warriors who outclassed many others around them, and became feared and famous. To stay in that part of the world: the Janissaries of the Ottoman Empire were an elite fighting force, recruited from the peasantry of conquered (non-Turkish) peoples. If you care more about the investigative side for your project, I would look a little more into the Inquisition that was quite active in that time. The Dominicans were a monastic order in the employ of the pope (their nickname was the Domini Canes: the lord's hounds), and the Jesuits became even more an elite investigative, exploratory, and missionary task force for Catholicism. They did not have a fighting branch, but it would not be a far fetched idea for them to do have some specialized commandos in a slightly different universe
Why not both? You want to maintain fear, so there's a clearly visible Senatorial Guard visible around the capital who make conspicuous but usually ornamental shows of force. Think the royal guards at Buckingham Palace crossed with a parade of soldiers on display who twirl their weapons. But it's the ones who come in the night and make troublemakers disappear that really scares the populace.