Mahavastu Kallimakus was a remembrancer who served as the personal scribe of Magnus the Red, Primarch of the Thousand Sons, during the Great Crusade. He was the author of the Book of Magnus, the Crimson King's great tome of sorcery.[1a] In his role as Magnus' personal remembrancer, Kallimakus was also present at the Council of Nikaea.[1b]
Shortly before the Space Wolves' invasion of Prospero, Kallimakus realized that his writings were a series of mystic rites (some of which he didn't even remember writing)[1a] and fled Prospero with his works on the mass conveyor Cypria Selene along with the remembrancers Lemuel Gaumon and Camille Shivani and Shivani's lover Chaiya Parvati.[1c] The ship was intercepted by the Hrafnkel on the edge of the system. Kallimakus was split up from the others during questioning.
After his casting of the Rubric and his exile by Magnus, Ahzek Ahriman — the former Chief Librarian of the Thousand Sons - remembered the works of Kallimakus, and began a 1600-year search for them. In time, Ahriman's search brought him to the world of Appollonia. Kallimakus was long dead, but a fanatical cult had arisen as guardians of his works, gathered in a great library known as the Athenaeum of Kallimakus. After a month-long siege, Ahriman and his Rubric Marines defeated the wardens of the Athenaeum, and Ahriman plundered the sorcerous works within before burning the library to ashes, so that only he would know the secrets within.