Astraeos was a Librarian of an unknown Space Marine Chapter that in late M32 or early M33 was targeted for elimination by the Grey Knights under the orders of Lord Inquisitor Castus Izdubar, following the loss of the Athenaeum of Kallimakus at Apollonia. He, and three other members of his Chapter survived -- its former Chapter Master, Thidias, its Chapter Standard Bearer, Kadin, and another Astartes, Cadar. They secured transport on a rogue Adeptus Mechanicus ship, the Titan's Child, under the captaincy of a rogue tech-priest, Carmenta, and fled for the Eye of Terror. Entering the Eye the ailing vessel was captured by the Harrowing, a band of Chaos Space Marine renegades. Cadar was killed in the assault and turned into a daemonhost by one of the Harrowing's sorcerers, Maroth, who removed one eye from each of the other three exiles. However a member of the Harrowing was the exiled Thousand Sons' former First Captain, Ahzek Ahriman. When an envoy arrived from the sorcerer-lord Amon seeking Ahriman, Ahriman revealed himself and sought Astraeos and his fellows as well as Carmenta to be his allies. Astraeos, not knowing who Ahriman really was, put his trust in the revealed sorcerer and became his most devoted pupil, and took his revenge on Maroth by taking the eyes of the sorcerer. Astaeos would be troubled by the daemonhost of Cadar, but chose to not reveal this at first to Thidias and Kadin. Ultimately he bound the Daemon to himself. Eventually Thidias was lost and Kadin learned of Cadar's host, but the remaining two exiles continued to support Ahriman. Lacking a Navigator they went to the border of the Eye of Terror and captured an individual named Silvanus from an Inquisition ship in which the Inquisitor Iobel was also on. Though Ahriman was severely wounded in the ensuing battle by the Inquisitor, his plan ultimately succeeded, and Astraeos, Kadin and the daemonhost Cadar helped Ahriman take control of Amon's warband. Despite their initial tensions, the homeless Astraeos and Kadin became Ahriman's most loyal warriors in the years that followed.
Ultimately Astraeos was sent by Ahriman to be captured by the Inquisition so that the sorcerer-lord might capture Inquisitor Iobel, who he believed knew the location of the Athenaeum of Kallimakus. His memories were burned and hidden, making the former Librarian and sorcerer take up the time and energies of the Inquisition. Astraeos was tortured, including by a Grey Knights Brother-Captain, Cendrion, but managed to escape his imprisonment at his trial before the arrayed members of the Ordo Malleus. Ahriman had planned this, and struck at the assembled Ordos so as to kidnap Inquisitor Iobel. Whilst successful in this regard, Astraeos was struck down and thought dead by the members of Ahriman's coterie, including Kadin. Kadin subsequently thought himself the last of his Chapter, becoming even more dedicated to Ahriman.
In truth, Astraeos was blinded, blanked and linked to a cyber-skull and further interrogated by the Inquisition under Lord Izdabar. He would reveal the hunt for the Athenaeum and the Inquisition would race Ahriman to Apollonia, where it was held -- having presumed that just as they broke Astraeos, Ahriman would have broken Iobel. At Apollonia, however, an implanted shard of Ahriman provided Astraeos with the energy to escape and revealed to him that it was the Inquisition, and its Chapter-militant the Grey Knights, who had purged his Chapter. Offered revenge by the fragment of Ahriman, Astraeos took it and went on a blind and psychically-empowered rampage throughout the Inquisition flagship.
When confronted by four Grey Knights Astraeos was mortally wounded in the subsequent fighting. As he lay dying he was called upon by the daemon within Cadar's body, who he had long ago bound to himself but never called upon, and was empowered by it. However, Astraeos also realised that his fate, and that of his Chapter, had been caused by Ahriman. In helping Ahriman and in encountering the Grey Knights he set in motion the demise of his Chapter, which occurred subsequent to Ahriman's successful theft of the Athenaeum. In entering the Eye, Astraeos, Carmenta and his comrades had gone into the past. Astraeos began planning revenge, stepping into the Warp to escape the flaming ruins of the Inquisition ship.
Sometime later at a temple on an unknown planet two Thousand Sons sorcerers led by a third Calitiedies, with the heads of serpents, hawks and jackals on their helmet, and their warriors met with a sorcerer in bronze who, "...bore the marks of ancient lore on [his] armour, and knowing the words of passing from ancient Prospero." The strange, crypto-Prosperine sorceror revealed himself: "I am Astraeos, and your oaths will be mine."
- Ahriman: Exile (Novel) by John French
- Ahriman: Sorcerer (Novel) by John French