Though the Blood Ravens have a long and glorious history of service to the Emperor, their exact origins and earliest days in the service of the Imperium are obscured and uncertain. Not even their Chapter Master or Librarians can say with any certainty when the Blood Ravens were Founded or from which of the First Founding Astartes Legions the Chapter is descended. The Chapter's written records in its Librarium only go back to the 37th Millennium, though vague references of their service in the litanies of other Chapters and Imperial Adepta prove that they existed and fought the enemies of the Emperor for many centuries before then. However, the records mentioned are either missing or locked away under an Inquisitorial Seal. The gaps in the Imperial records concerning their origins are so extensive that the Chapter does not even know the origins of its gene-seed or their father Primarch. The fact that the Blood Ravens' own records and Chapter lore are lost along with those kept by the Inquisition on the Chapter is a suspicious indicator that suggests that a concerted effort was made by operatives within many Imperial Adepta, including the Inquisition and the Blood Ravens themselves, to eliminate almost all trace of the Blood Ravens' past from Imperial records. Why this erasure was carried out remains unknown but the event is known as the "Un-Founding" by the Blood Ravens. What is odder still is that records on the Blood Ravens were discovered on Eldar knowledge worlds hidden in the Eye of Terror and guarded by the enigmatic Harlequin. The Blood Ravens prize the pursuit of knowledge greatly, but ironically the Astartes of this Chapter know little about their own origins or the earliest centuries of their service to the Emperor of Mankind.