Kabr was a Titan who had fought during the Battle of Six Fronts. He was inspired by Osiris, and assembled a fireteam to strike at the Vault of Glass. His fireteam was wiped/erased in the Vault, including the Warlock Praedyth. He was driven mad by the realization that he couldn't have infiltrated the Vault alone, but he had no fireteam members that he could remember. Pahanin, a Hunter who knew him, witnessed his fall into insanity and 'Vex sickness', and created the Super Good Advice to keep him company. Kabr discovered many of the Vault's secrets, but was infected with the Vex. He lost his Ghost, and was face with the fact that he would either die or become something else. He pierced the Vault and let in the Light, and fashioned the Aegis out of his Light and the thinking flesh of a Gorgon. He was corrupted by the Vex, and vanished into the depths of the Vault. During the battle with Atheon, the Aegis binds every possible timeline of the fight into one event. Every single fireteam that ever fought, is fighting, will fight, or could have fought Atheon was firing at him at the same time, allowing you to bypass his immense shields and health and kill him