It was Malcador who convinced the Emperor of the necessity of creating a new force of Space Marines specifically tasked with fighting the threats of the Warp. The Emperor would later concede He had made a mistake when He created the original Legiones Astartes, for they had been intended to fight the threats to humanity found only in the physical realm, and not the far worse horrors of the Immaterium.

The Emperor had believed that the Ruinous Powers would not be able to interact with the physical realm as easily as had proved the case or to corrupt His most powerful servants with such little effort. The creation of the new corps of psychic Space Marines was intended to remedy this terrible oversight.

Among the twelve individuals Malcador had presented to the Emperor in the days before the Siege of Terra when he took the Master of Mankind's place upon the Golden Throne were many of those who had already served the Imperium well. Eight of the twelve were Astartes drawn from both the Loyalist and Traitor Legions. These included many of the most prominent of his own Knights-Errant, including Tylos Rubio, Macer Varren, Janus, Epimetheus, and Khyron. Among the mortals were the former Iterator Kyril Sindermann, the former Remembrancer Lemuel Gaumon and the Silent Sister Amendera Kendel.

After they were presented, the Emperor gave His approval, noting that Malcador had chosen well and the project shoud continue. Malcador had decided to split the group up to deal with the very different tasks set before them; the four mortal lords were kept separate from the Astartes and moved to lay the framework of what became the early Imperial secret police force known as the Inquisition while the Space Marines travelled with Malcador through a Webway portal to the moon of the gas giant of Saturn known as Titan.

Through the use of Malcador's abilities, Titan had been cloaked from the ravages that had befallen the Sol System during the battles of the Horus Heresy. The eight Astartes discovered that a great fortress-monastery had already been established on Titan's frigid methane plains, stocked with all the supplies, materiel and vehicles needed to create a new Space Marine force. This included stockpiles of gene-seed drawn from an unknown source whispered to be the Emperor Himself.

The fortress was already filled with thousands of Aspirants drawn from locations across the galaxy, many untrained while others had once been selected for service with the remaining Loyalist Legions, though every single one was a psyker. The new Space Marine force would be organised not as a Legion, however, but as a Chapter, a smaller, more focused army only a few thousand Astartes strong. As Malcador needed to return to Terra immediately to carry out his last duty for the Emperor and Mankind, he chose Janus to serve as the first Supreme Grand Master of the new Chapter, which was to be called the "Grey Knights."

As he left, Malcador cast his last and greatest psychic enchantment. The entire moon of Titan was hidden within the shifting tides of the Immaterium, shielded from its many dangers by Macro-Gellar Fields and sigilic rites of protection that had been prepared on the moon beforehand. In this way, Titan and its Grey Knights were protected from the final battle of the Horus Heresy while Janus and his seven comrades built and organised their new Chapter safely within the Warp. Titan finally emerged into the Immaterium approximately a thousand Terran years later in the 32nd Millennium.

The Grey Knights, now a fully-forged Chapter dedicated to the defence of Mankind from the daemonic terrors of Chaos, contacted the Inquisitor Lastan Neemagiun Veritus, once known as Kyril Sindermann, to let them know they were ready to join the fight. In the wake of the War of the Beast, the Grey Knights would become the highly-classified Chamber Militant of the new-formed Ordo Malleus of the Inquisition.