Illum, called Ghaznavi by the children who see him walk through the fields, is the quietest dangerous person in the fiction. He is great at strategy — so great it unsettles the other main characters, including the C1 villain, who has not met many minds that can keep pace. He also suffers, always, from a failure of opportunism: unable to seize the moment cleanly, he is forever blaming what produced his situation and what is changing it. That gap — between what he can see and what he can bring himself to do — is the shape of his whole story.
The eye ¶
The virus Illum extracted was the same one Ghaznavi carried: the most intelligent strain, the one the hive itself defers to. It shaped his eye the way it shaped Ghaznavi's — red sparks radiating from the pupil in one eye. Chapter 2, the one he looked out of the window with. That eye is visual communication from the bacterium, showing him the weak spots of any target he is about to hunt. The other eye is the rational human one, holding him at bay. Most of the infected are possessed wholesale — every eye manipulated, or none. Illum is one of the very few who carry both at once.
The hive ¶
The children call him Ghaznavi because the hive-minded bacterium is calling him back. It communicates across long distances, and it signals when its hive is under attack. When Illum walks through the fields, he is arriving home. This is, likely, why in demon form he returns to the hive in the future arc — to protect them. The protector and the parasite are, by then, the same person.
The covert work ¶
Illum and Dreamgirl may have played an integral part in setting up the Grids — sensing and hunting down the remaining bacterium holders throughout the eastern combs. He is also one of three signatories of the Kafiristan Pact, alongside the Grid Philosopher and Vader's Grandfather: a covert team formed behind closed doors to uncover what Kafiristan actually is, through space travel and undercover missions on earth. They agreed Kafiristan could never be made into a Grid. They also agreed that a day would come when the Grids had to encroach on it — and they had to be ready.
Why he matters ¶
Illum is the hinge between the On-Grid Society and every threat sitting outside it. He is the human who carries the enemy inside him and uses it to protect the world the enemy is coming for. Judgement Day, when it arrives, arrives partly because of what he already knows.