The Order Elucidatum, whose agents were known as "Elucidators" or "Tallymen," was an agency of the Imperial government established during the Unification Wars by Malcador the Sigillite. They seemed to serve as functionaries of the Imperial Administratum but were in fact the Sigillite's secret police as the Imperium rapidly grew during the Great Crusade.
The Elucidators carried out operations of censorship and assassination to eliminate any threats to the spread and enforcement of the atheistic Imperial Truth that served as the foundation of Imperial culture in the Pre-Heresy era. In many ways, they were the forerunners of the later Imperial Inquisition.
In 012.M31 during the height of the Horus Heresy, the Order Elucidatum was formally dissolved by the Sigillite without fanfare, and records pointing towards its existence expunged. Those few Tallymen who survived to return to their master on Terra were not lauded as either heroes or villains but quietly inducted into different secretive Imperial agencies, for Malcador was still in need of proven men and women with their particular skills.
Many mysteries were unravelled in the aftermath of the Horus Heresy through investigation into the archives of the Sigillite. In the sealed underground archivum of Azure-Locus-CI-yAlpha, the preserved records of the activities of Malcador's secret police -- the so-called Officers of Elucidation -- were found; corroborating hearsay long dismissed as simple fear-mongering.
The Order Elucidatum, colloquially known as the "Elucidators" or less respectfully as the "Tallymen," acted in two functions; openly as apparent contributors to the bureaucracy of the Great Crusade and covertly as iconoclasts, censors and assassins.
In their open and official capacity, the Elucidators travelled freely among the Expeditionary Fleets of the Great Crusade, operating as supporting data scribes to the offices of Iterators, future Planetary Governors and census takers as a function of the Administratum.
The work of the Elucidatum was vital in sifting and analysing the data gathered from the newly Compliant civilisations; categorising, scrutinising and providing useful demographic information to those now in command, or gently guiding the rhetoric required of Iterators to bring about more efficient transitions to Imperial authority.
The unfettered access the Order had in regards to the databanks of combined knowledge of the Great Crusade was instrumental to their ulterior and true purpose for being abroad in the galaxy. By analysing census data and being privy to the information provided by the ambassadors of newly-found human worlds, the Elucidators could determine the risk posed by nascent or suppressed religious cults to the Imperial Truth on those worlds post-Compliance.
This information facilitated the pursuit of their true objectives: the assassination of demagogues, the destruction of proscribed texts and the suppression of any persons with knowledge of or contact with the manifestations of the Warp. The mandate possessed by the Order Elucidatum was underwritten with the seal of the Sigillite himself, allowing the Tallymen, who were themselves expert and highly specialised warriors, to take immediate possession of any Imperial military unit or asset they required, other than the Legiones Astartes, to complete their mission.
These missions were chosen and undertaken independently, for the Sigillite had recruited highly intelligent warriors from the finest military orders in the Sol System for his secret police, as part of the earliest of his initiatives to find men and women of inquisitive nature who might seek out traitors, spiritualists, witches and those tainted by them. The Elucidators held no trials, trusting to the logic of the Imperial Truth and the insight of the information they compiled in selecting the targets of their "elucidation."
Though few truly knew of the exploits of the Elucidators, they earned a dark reputation. They were a faction responsible for the burning of churches, temples and other fanes with all of their worsjippers still huddled within, and the pogroms of religious castes in the rural wilds of countless worlds. Their name quickly became synonymous with genocide.
Malcador's secret police were sanctioned to make use of seratoxin, a nerve agent dispersed to ensure that the minds of all witnesses of any kind of immaterial incursion event -- man, woman or child -- were utterly expunged and placed beyond any hope of recollection. A cruel fate, the so-called "Brain Destroyer" left its victims as withered husks, unable to respond to more than autonomic instinct and phototropic cues.
Their atrocities were not limited only to the murder of entire lines of Imperial households, for as the great Crusade advanced into the farthest reaches of space, it was the Elucidators who took it upon themselves to wipe out the many early cults of Emperor worship within the Expeditionary Fleets. The Tallymen became a Bogeyman or Chowkidar to be feared in the minds of common folk residing in the bellies of the vast warships of the Great Crusade, with elders admonishing misbehaving children by invoking their name.
Had Mankind been trusted to know of the Warp's true nature and reject it of its own volition, the Order Elucidatum would not have been needed. Thousands upon thousands of deaths and the massacres of innocents simply accused of association or belief in Warpcraft without due process could have been avoided. Their tally of murders is a direct contribution to the cost of maintaining the falsities of the Imperial Truth.
- The Horus Heresy Book Eight - Malevolence (Forge World Series) by Neil Wylie and Anuj Malhotra, pg. 26