Cloaked Brothers

“All that stuff about Cloaked Brothers is bunk. Like the Skaven, they don’t exist.”

—Kleber Reinhard, Witch Hunter

The mysterious Cloaked Brothers are a splinter group of the Templars of Sigmar. Instead of killing and burning, they exist to gather information and spy. They are under no compulsion to kill Mutants or cultists, merely to look, learn, and report to their masters. It's not clear when the Cloaked Brother emerged as an organisation, but their level of penetration into Imperial society suggests they’ve been around for a while. Throughout their existence, they’ve remained hidden and are nothing more than rumour and myth. They surfaced during the year leading up to the Storm of Chaos. Having insinuated themselves inside Luthor Huss's Crusade, they fed a steady stream of information about the search for Sigmar reborn, as well as Huss' movements throughout the countryside.

After the Storm of Chaos, the Cloaked Brothers faded back into anonymity. Whilst it's presumed they are still active, there has been no known contact with the agents since Valten's disappearance.

Cloaked Brothers are hidden agents loosely affiliated with Sigmar's Witch Hunters. Though not a true branch of the Templars, they often have cause to join forces with their, sometimes overzealous, brethren. However, they are just as likely to double cross them as they are with any organisation they deal with. Cloaked Brothers are masters of information. They infiltrate organisations to learn what they can, reporting their findings to their superiors—though who exactly "they" are is unknown. This organisation draws from a vast array of talent, from ex-Witch Hunters to Mutants.

Source

 * Warhammer Fantasy RPG 2nd ED -- Tome of Corruption pg. 126