All of the Chapters derived from the Blood Angels still suffer from the psychic imprint left by Sanguinius's death. This can cause them to go insane prior to or during a battle, and they believe that they are Sanguinius himself during the Battle of Terra. The condition is irrevocable (except for one case, Chaplain Lemartes, who is largely able to control it), and victims are locked away in the "Tower of the Lost" on the Blood Angels' homeworld until they finally die. This insanity is known as the Black Rage. When a Space Marine is overcome by the Black Rage he is reborn in a world of anger, hatred, fury and nothing else. As well as Sanguinius’s memories, the Blood Angel is touched with a small portion of his unearthly power, boosting his strength and vitality to superhuman levels.
Rather than face a slow, insane death, Blood Angels will form those who have newly succumbed to the Black Rage into a special unit known as the Death Company. They paint their armour black, daubed with red crosses, signifying the wounds of Sanguinius, and are usually led by the few Chapter officers, notably Death Company Chaplains, who are able to communicate orders to these lost warriors. They are then sent out to perform the most dangerous assaults, hoping for a quick and honourable death in combat.
Fortunately for the Blood Angels, the new wave of Primaris Space Marines seem able to more easily resist the Red Thirst, while showing no signs of the Black Rage at all. However the Primaris Marines may not be as resistant to The Flaw as once thought, as evidenced by the Khovan Incident.