The Blood Angels and their Successor Chapters of Loyalist Space Marines still suffer from a genetic flaw that creates mental instability called the Black Rage, also known as the "Flaw of Sanguinius", as a result of the psychic imprint left by their Primarch Sanguinius' death at the hands of Horus during the Battle of Terra.
Blood Angels are unique amongst the Space Marines in that deeply engrained in their gene-seed is the encoded experience of their Primarch, and most deeply imprinted of all is the memory of Sanguinius' final battle with Horus. Sometimes, on the eve of battle, an event or circumstance will trigger this "genetic memory" and the Battle-Brother's mind is suddenly wrenched into the distant past. The Black Rage overcomes the Blood Angel as the memories and consciousness of Sanguinius intrude upon his mind, and dire events ten thousand Terran years old flood into the present.
This can cause Blood Angels Astartes to go insane prior to or during battle and feel the uncontrollable rage of Sanguinius himself during the final days of the Battle of Terra. The condition is largely irrecoverable and only a few Blood Angels have managed to overcome "the Flaw." Victims are locked away in the Tower of Amareo (named after an ancient Chapter Master of the Blood Angels), also called the Tower of the Lost, on the Blood Angels' homeworld of Baal in their fortress-monastery complex of the Arx Angelicum.
The reason the Black Rage can be suffered by Blood Angels who have never been in proximity to their long-dead Primarch is that during the battles of the Horus Heresy on Terra and Mars, the Blood Angels' stores of gene-seed were lost. To reconstitute the Blood Angels Legion in the immediate aftermath of its terrible losses during the Heresy, gene-seed had to be created from new genetic samples removed from the body of Sanguinius. As a result, every Blood Angel inducted into the Chapter since that time has run the risk of falling to the Black Rage and reliving Sanguinius' final moments before his murder by Horus.
A warrior overcome with the Black Rage appears half-mad with fury; he is unable to distinguish past from present and does not recognise his comrades. He may believe he is Sanguinius upon the eve of his destruction, and the bloody battles of the Horus Heresy are still raging all around him. Such a Battle-Brother stands at the end of his travails, for his path leads only to the Death Company, where he and the Chapter's other damned souls will fight one final battle in Sanguinius' name.
When a Space Marine is overcome by the Black Rage he is reborn into a world of constant anger, hatred, fury and nothing else. As well as Sanguinius' memories, the Blood Angels and their kin are genetically touched with a small portion of the Primarch's unearthly power, boosting their strength and vitality to superhuman levels. Rather than let them face a slow, insane death, the Blood Angels and their Successors will form those of their Battle-Brothers who have newly succumbed to the Black Rage into a special unit of the Chapter known as the Death Company. They wear specially painted black Power Armour, daubed with red crosses to symbolise the wounds of Sanguinius and are often led by the few Chapter officers, notably Chaplains, who are able to communicate orders to the insane troops. They are then sent out to perform the most dangerous assaults, hoping for a quick and honourable death in combat.
However, by some unknown means, the genetic flaw in the Blood Angels' gene-seed that produces the Black Rage also seems capable of extending the victim's lifespan, at least until he finally succumbs to the Rage. Lord Commander Dante, the Chapter Master of the Blood Angels, is by far the oldest living Loyalist Space Marine (not including those interred in a Dreadnought), born more than 1000 Terran years before the present time, a feat that may only have been possible because of the genetic flaw he bears.
Blood Angels Freed From the Flaw
- Mephiston - Originally Battle-Brother Calistarius, a Blood Angels Librarian of some considerable ability and strength of character, Calistarius was almost overcome by the Curse of the Black Rage when he served as part of the relief force for Hades Hive during the Second War for Armageddon, where, having suffered for 7 solar days and nights trapped in the rubble of the collapsed Ecclesorium building, a vision of Sanguinius helped him fight off the effects. He was reborn as Mephiston -- the Lord of Death, and with his full psychic potential unlocked, quickly achieved the position of Chief Librarian for the Blood Angels Chapter. He is seen as the spiritual son of Sanguinius, a figure of hope to his Chapter. He is now considered to be the most powerful Librarian in the Adeptus Astartes, and possibly the most powerful psyker in the Imperium, after the Emperor of Mankind.
- Rafen - A Battle-Brother -- later promoted to Sergeant -- Rafen had to kill his brother Arkio who was claiming to be Sanguinius reborn but was in reality deceived by Chaos, having been made, through mutation, into a likeness of Sanguinius. Rafen then had to succumb to the Gene Curse to unleash the power of the Holy Spear of Telesto (a weapon wielded by Sanguinius himself) in order to defeat Malfallax, a Lord of Change who had deceived Arkio. However, he was eventually able to pull himself to the surface of his consciousness, and also succeeded in helping Mephiston defeat the Black Rage within himself a second time. Rafen was the protagonist of the Blood Angels series of novels by James Swallow.
- Codex Adeptus Astartes - Blood Angels (8th Edition), pp. 12-13
- Codex: Blood Angels (5th Edition), pp. 12-13
- Imperial Armour Volume Two - Second Edition: War Machines of the Adeptus Astartes, pg. 167
- Index Astartes I, "Blood Frenzy - The Flesh Tearers Space Marine Chapter"
- Index Astartes II, "Angels of Death - The Blood Angels Space Marine Chapter", pp. 34-37