Harrowmaster was a Praetor-level rank of the Alpha Legion Space Marine Legion during the period of the Great Crusade and the Horus Heresy in the late 30th and early 31st Millennia. A Harrowmaster was often given command of all the Alpha Legion forces deployed to a given theatre of operations. It is unknown if this rank is still in use by the Heretic Astartes of the Alpha Legion in the late 41st Millennium.
In terms of honorifics and titles, the Alpha Legion seemed to have used a shifting set of terminology to convey authority and role. At times the Alpha Legion appears to have deliberately aped the systems used by other Legions (such as the Sons of Horus and the Blood Angels) although whether this was done to incorporate a proven pattern of organisation as part of a particular strategy or as some form of mockery remains unknown.
Aside from these patterns, close scrutiny of the records also reveals several distinctive additional divisions of command not shown by other Space Marine Legions. One such unique title known to have been used by the Alpha Legion was that of "Harrowmaster" or Jhariuk as the leading commander given overall control of all Alpha Legion forces in a given war zone.
Although their nominal rank might vary, it was the task of the Harrowmaster to keep track of encompassing the shifting events of a conflict in minute detail and shape the actions of the Legion's forces accordingly, creating and aborting battle plans and stratagems with bewildering speed. The position of Harrowmaster was known to be held as a supreme accolade by the Alpha Legion, and their infamous skill at battlefield control was highly regarded (even as the Legion itself was often mistrusted) by the commanders and stratagos of the other Space Marine Legions.
It is noteworthy that the Harrowmasters were among the few of the Legion, save its Equerries, whose personal names are left to the open record, although whether these have any basis in reality or were merely guises worn by a single warrior or perhaps a series of individuals to hold the same rank remains unknowable.
- Armillus Dynat - Known as the "Griefbringer" and "Instar-Nine," Armillus Dynat was a Harrowmaster of the mysterious Alpha Legion during the Great Crusade and Horus Heresy eras in the 30th and early 31st Millennia. Dynat was a feared strike commander since his name came to prominence during the invasion of Paramar V. Known to possess strategic genius, his style of warfare was as intricate as it was unorthodox. Using fast moving, heavily-armoured vehicles and close air support, he would split enemy formations apart before crushing them without mercy. Armillus Dynat was an expert duellist and warrior in his own right. Wielding a Thunder Hammer and Power Sword in unison and carrying uncommon wargear such as Venom Spheres and Phosphex Bombs, he was an opponent to be reckoned with.
- Kel Silonius - Silonius was a favorite commander of Alpharius himself whose identity was used by the Alpha Legion Primarch to infiltrate the Sol System and Terra itself to begin a campaign of sabotage and guerilla warfare against the Imperium at its very heart. Later, Silonius led the Alpha Legion fleet of over 200 warships that invaded the Sol System during the Battle of Pluto and ordered its retreat at battle's end after the seeming death of his Primarch at the hands of Rogal Dorn.
- The Horus Heresy - Book Three: Extermination (Forge World Series) by Alan Bligh, pp. 25, 29-30, 90, 262
- Praetorian of Dorn (Novel) by John French