Malvoisin was an Angels Resplendent Chaplain, who Sergeant Montaig brought the Undying Martyr to, after discovering him near their Fortress Monastery. The Martyr would then go on to turn the Chapter into the Angels Penitent.
This occurred when the Undying Martyr was interrogated by Malvoisin who would determine his fate. This proved to be a significant decision for the Chapter, as despite bearing a fatal looking chest wound, the Martyr was able to talk to the Chaplain for days. It was during that time, that he convinced the Chaplain that Mankind was corrupt and the war to save the Imperium was lost. The Martyr declared that the Space Marines were the greatest sinners of all, which was made obvious by their failures during the Horus Heresy. There was now no hope left in the galaxy - only penitence and pain for sins committed in the past and future. After the 19th day of their discussions, Malvoisin declared to the Angels that the Martyr was a prophet of the Emperor. This caused the Chapter to listen to his words and with their Chapter Master, Varzival, away campaigning, no one could stop the Angels from falling under the Martyr's sway. He became their spiritual leader and declared the Chapter to be too prideful and vain. The Martyr demanded they destroy everything that tied them to their sinful past and the Great Purge began. Gripped in self-hatred by the Martyr's revelations about their Chapter, most of the Angels did as he commanded asked, with only the Librarians refusing to follow his orders. This led them to become targets for the Chapter's wrath and Chaplain Malvoisin led a group of Battle Brothers against them. When Malvoisin's group went to attack, however, Chief Librarian Athanazius and the other Librarians, did nothing to defend themselves. Instead Athanazius uttered the Resplendent's battle cry, "We will rise on burning wings". This brought the attacking Battle Brothers to a stand still, until Chaplain Malvoisin, yelled out the Penitent's new battle cry, "The Emperor Condemns". This roused the hatred of the attacking Battle Brothers once more and the Angels Penitent were born with the Librarians' deaths.