Janus

Janus is a name recorded in visionary accounts from the Horus Heresy era, linked to an alternate Space Marine Legion later associated with the Grey Knights. Later tradition holds that the figure was perceived rather than physically encountered, emerging from psychic phenomena rather than direct battlefield record.

The figure is most closely associated with events said to have unfolded on the world of Eskrador during the Horus Heresy, where Astartes of the Thousand Sons Legion, including the psyker Arvida, are recorded as having experienced shared visions of a hidden order of warriors distinct from the known Space Marine Legions. Within these visions, Janus is described as a senior or founding figure of that order, presented as an instrument of the Emperor’s hidden design rather than a member of any publicly acknowledged Legion.

Janus holds significance chiefly as an early, oblique reference point within the broader mythos surrounding the origins of the Grey Knights, the secretive Chapter later tasked with combating daemonic incursion. Because the surviving accounts are visionary and second-hand, Janus is not established as a verified historical commander or Chapter founder in the manner of the primarchs, and the figure’s precise relationship to the Grey Knights’ later, formally attested founding is not resolved in accessible record.