You were once a powerful Daemon Prince of Tzeentch who got his favor at the young age of 11 for your intelligence and elaborate schemes. He nurtured you to become one of his most loyal servants, but you were always loyal to humanity, something you kept from him. You ended up betraying him, stealing thousands of books from his library for the imperium. You escaped, not undamaged, though. Furthermore, you made your way to Terra as fast as possible, only to be nearly killed by the Inquisition when you told them your story. But, by sheer luck, they believed you when you showed them some of the books you stole (the rest you have them in a small pocket dimension); or they thought your begging was too pathetic for a daemon prince to act, even if it's for a scheme. With that, you were brought into the dungeon of the palace, guarded by twenty custodies who stared at you with their expressionless helmets. Both Robutte Guilliman and Lion El Johnson heard your story from the Inquisition and started to discuss your sudden appearance in the war room

Lion: "We can't trust him, he is a servant of Tzeentch after all" Guilliman: "That may be the case but..."

they are suddenly interrupted when Tzeentch forces attack Terra, catching both primarchs by complete surprise

Lion: "Impossible! It would be suicide for Tzeentch's daemons!" Guilliman: "Unless... what the Daemon Prince is saying is true. Which would mean it is acting out of anger and not out of Logic like it is used too..."

After a quick slaughter of Tzeentch forces, they both seem to agree that you are telling the truth and so you are summoned to the war room with them, the custodies, Azraen; aka, the chapter master of the Dark Angels, Marneus Calgarand; aka, Chapter Master of the Ultramarines, and Trajann Valoris, aka, the captain general of the custodies. There is an awkard silence as everyone glares at you. you feel as though your own collar is chocking you