Much like Captain Angelos, Brother-Librarian Isador Akios was born and raised on Cyrene, and became a Blood Raven around the same time as Gabriel because they were brought up together. Isador met Gabriel 30 years before the events on Tartarus when Gabriel was still a battle brother. Although his homeworld was destroyed, Isador did not blame Gabriel for his actions on Cyrene, since it had to be done. While the Blood Ravens 3rd company was on the doomed planet of Tartarus, Isador slowly succumbed to the powers of Chaos, tempted by the traitorous Sorcerer of the Alpha Legion named Sindri Myr, telling him of the "Key", and tempting him to use it. When Inquisitor Mordecai Toth arrived, he detected a Chaotic taint and came up with the assumption that it originated in Gabriel. Because of this, they were blinded to Isador's corruption and thus, could not stop Isador before he finally seized the Maledictum and turned to Chaos, bringing Gabriel's trust in his old friend crumbling to the ground.
Isador was killed in a duel between himself and Gabriel, and Gabriel used his death as an example of the fate of Space Marines who fell to Chaos. Isador was armed with a Force Weapon and Bolt Pistol. He was able to be upgraded with a Plasma Pistol later on in the campaign