Chapter records state that the first Astartes to bear the name Sons of Corax once belonged to the Raven Guard Third and Eighth companies that were still struggling to recoup their losses following the Horus Heresy. Captain Taimon Naskius of the Raven Guard Eighth was chosen by his Chapter Master to lead the newly formed Sons of Corax and continue to protect Humanity. In the age of the Imperium’s rebirth from the ashes of its devastating civil war, Space Marine forces were needed more than ever. Several new chapters were sanctioned for the Third Founding and they took part in some of the bloodiest battles in Imperial history. Captain Naskius took the title of High Commander, a former legion rank often bestowed by the Primarch Corax upon the most preeminent fleet captain. The Sons of Corax were gifted with the battle-barge Montisgarre, a warship of the Great Crusade that had served since the Heresy as a training vessel in the Deliverance system.
High Commander Naskius established the Sons as a crusading chapter and chose the Tempestus Segmentum as his eternal warzone. In the early years of their founding the Sons worked frequently alongside their predecessors the Raven Guard and several newly commissioned Imperial Guard regiments. The Sons established cooperative pacts with many of these regiments and cemented their ties to Raven Guard. Over the years the Sons have exchanged many battle honours with their allies and the Vault of Conquest aboard Montisgarre is home to the battle standards commemorating their victories. They have earned recognition across the entirety of the Segmentum for their dedication and loyalty as well as their relentless persecution of all enemies of the Imperium.
Yet for all their nobility and their glorious battle record they have had their moments of ill-repute and campaigns that have failed. During the Frannos Heresy of 119.M37 the Chapter slaughtered hundreds of thousands of civilians of Orlin IV in order to capture the traitorous Cardinal Frannos. The Ordo Hereticus demanded custody of the prisoner but the Sons refused and executed the Cardinal publicly, an act of defiance that earned them bitter enemies amongst the Ordo. This and other incidents have created mutual distrust between the Ordo and the Chapter and the Sons have ever avoided Inquisitorial control. Given the political connections cultivated by the Chapter, the Ordo Hereticus has avoided open confrontations, preferring to work covertly.
In 533.M39 the chapter participated in an Imperial campaign to drive out the forces of Chaos in the Becoun subsector and reclaim it in the name of the Emperor. However, incompetent leadership and political infighting doomed the campaign from the start with initial victories overshadowed by one disastrous defeat after another. The 8th and 9th companies who had taken part in the campaign suffered crippling casualties and were forced to withdraw three years later lest they be wiped out completely. Over a hundred and fifty battle-brothers had been lost and it took the chapter nearly seven decades to bring both companies back to full strength.
Over the millennia, the Sons of Corax have fought a great many different foes but of all of them they prefer most to fight the renegades and traitors of the Chaos Space Marines. The Chapter nurses a particular hatred for the Betrayers of Isstvan, the Traitor Legions of the Iron Warriors, Alpha Legion, Night Lords and the Word Bearers. The Sons have brought many of their enemies’ followers to justice and their fury when dealing with these accursed followers of Chaos is unmatched.