Chekist
Chekist is a secret police force in Kislev, based on a Soviet secret police called Cheka or the various Tsarist organizations that came before it. As you have probably guessed, their main duty is to protect royal family. By any means. They have no official organisation aside from the fact they're all recruited by Tzarina, and most of the time they travel around the country, dealing with Chaos cults, criminals and spies in a manner of Judge Dredd. Whatever the Chekist say the law is, is the law, remember.
Unlike their real-life prototypes, however, they are not as cruel, and while they can arrest and torture people according to their own Chekist beliefs, extremely ruthless ones are removed by their superiors... unless they're extremely competent, and in that case they're usually rotated from one corner of the country to another, to prevent unwanted accidents.