A'gaeris was the primary agent behind the fall of D'ni.
He was a member of the Guild of Writers around 9340 but was accused of a number of crimes including stealing a book, although he denied the charges. Expelled from the guild, and his betrothal broken off, he went to live in the lower city, in the Kerath'en District.
Over the next fifty years A'gaeris established a name for himself as a writer of influential pamphlets, becoming known as the Philosopher. He wrote of his opposition to ahrotahntee and especially to interbreeding (as in the case of Gehn). In reality, however, his goal was the complete destruction of D'ni in revenge for his punishment.
A'gaeris's chance came with Veovis and he used their mutual friend Suahrnir to meet with him. Secretly he planned to frame Veovis and induce in him the bitterness he himself felt. A master forger, A'gaeris wrote documents in Veovis's own handwriting to implicate him of trading in illegal books, and killed two young Maintainers with a dagger belonging to Veovis. He then provided evidence to Veovis's former friend Aitrus, starting the investigation that would lead to Veovis being sentenced to a Prison Age.
A'gaeris freed Veovis and together with Suahrnir they plotted terrorist attacks on D'ni, including the bombing of the Ink-Works and the desecration of one of the Five Classics with additions in Master Talashar's own handwriting. However, the Age they used as their base was discovered by Anna and Veovis fell back into the hands of the Council. A'gaeris fled and, using natives of an Age as his slaves, was able to release Veovis from his new prison.
From their new bases, K'veer and Veovis's Age of Ederat, they plotted again. This time they succeeded with a plague in the form of a dark cloud that spread through the cavern killing everything it touched. They spread it through as many Ages as they could find by sending dead bodies through Linking Books. With this accomplished, A'gaeris asked Veovis to write an Age where they could be gods. This line was one Veovis refused to cross and A'gaeris stabbed him in the back. Discovering Anna and Gehn in the city, A'gaeris took them to K'veer as bait for Aitrus and a final act of revenge. But a dying Veovis had provided Aitrus with a link so he could arrive ahead of A'gaeris and alter Ederat so that it became an inferno of molten rock. Aitrus lured A'gaeris into the Death Book and both perished there.