Casan Sabius is a Red Scorpions Captain and, since the internment of Carab Culln into the shell of a Leviathan Dreadnought, he has become one of the two de facto Chapter Masters of the Chapter, alongside Sirae Karagon.
Sabius is renowned amongst his Chapter, as being a formidable strategist and swordsman. These skills aided him when Lord High Commander Culln, fell in combat against the Hive Fleet Kraken beast known as the Great Beast of Sarum and the Red Scorpions rallied around Sabius' leadership as the Hive Fleet began to overwhelm them. In order to save his Chapter from being destroyed, Sabius took command of the Red Scorpions' fleet and enacted a flawless strategy of disengagement from the tendrils of the Hive Fleet, whilst also coordinating a precision orbital bombardment that allowed them to escape. Afterwards, Culln was interred within a Leviathan Dreadnought and command of the Chapter fell to Sabius, who his Battle Brothers deemed worthy to lead them. However he does not share their belief. Sabius secretly feels responsible for the loss of Culln, whom he so admired, and only now reluctantly leads the Red Scorpions as its Lord-Regent, until the Chapter selects a new Lord High Commander.
During a battle, Sabius can always be seen fighting on the front lines, where his bravery and determination leads him to slay the most dangerous foes with the Blade of the Scorpion. This always inspires great fervour in his Battle Brothers, who fight all the harder to seek out grander feats of glory to forge a legacy worthy of their Lord-Regent. However now, a need for atonement drives Sabius to serve his Emperor with greater zeal and he throws himself into the fray, lest his revered Chapter suffers further harm. This earnestness is mirrored in the Lord-Regent’s nigh-on fanatical pursuit of genetic purity, a traditionalist outlook that unites the battlegroups of the Chapter after the losses sustained in the Indomitus Crusade.