Rumours circulate that Abaddon, the master of the Black Legion, might be the clone-progeny of the Warmaster Horus, mirroring his primarch in his combat prowess and tactical skills. Other theories suggest that Abaddon's Humanity was lost due to his primarch's death and defeat at the Siege of Terra, leaving him filled with rage and hatred towards both the Imperium and his own primarch. An alternative belief is that he is a creation of the Dark Gods, embodying their disdain for Mankind. The truth of Abaddon's origins, beyond his former role as the first captain of the Sons of Horus Legion and a member of his primarch's advisory Mournival during the Great Crusade and Horus Heresy, is unknown.