Raptors are the debased heirs of the Legion assault companies, jump-pack warriors whose long corruption has twisted the honest ferocity of the Astartes assault trooper into something cruel and predatory. Where once they leapt into battle to break the enemy line, now they hunt for the sheer thrill of looking down upon lesser beings before they kill them. Vanity and sadism define them, and they have come to see themselves as apex predators, stooping upon their quarry from on high.
Centuries of exposure to the Warp have melded these warriors with their wargear. The machine-spirits of their jump packs have grown corrupt and hungry, and the boundary between warrior and machine has blurred until true flight becomes theirs to command. Their sight has sharpened to inhuman acuity, able to pick out a fleeing target across miles of open battlefield, and some are said to carry high-octane promethium in place of blood, fuelling body and pack alike. They strike with the force of falling meteors, crashing down amid the foe in a storm of chainblade and bolt.
Terror is as much their weapon as any blade. Altered vox-casters jut from their helms and battle-plate, amplifying their shrieking war-cries into a cacophony crafted to unman the bravest defender before the killing even begins. A warband looses its Raptors to sow panic and confusion, to run down fleeing survivors, and to descend upon isolated commanders and heavy weapons. They are the vicious, gloating huntsmen of the Heretic Astartes, and they delight in every scream they wring from the dying.