Cyrax. An obscure little world nestled within the vastness of the Ultima Segmentum. A ferocious home, known predominantly for its prime predator as the Wyrmworld. Wyrms are massive, two-legged beasts, their upper body lizard-like, yet possessing upper limbs resembling those of a monstrous avian. Though they are the largest inhabitants of the planet, they are far from its rulers.
It is human nature to spread to even the most inhospitable reaches and bend nature to their will. Primitive by Imperial standards, the local populace consisted mostly of tribes organised into large clans which fought contained, ritualistic conflicts in reverence of the God Emperor. The wyrms were no small part of this society, tamed for their brute strength as a symbol of status and power and even used in war, though their fiercely temperamental nature kept them contained on Cyrax only.
The recruiting world of the Golden Wyrms chapter of Adeptus Astartes. A successor of none other than the unnecessarily-revered Ultramarines, they were of those who looked upon the great Codex Astartes more... practically. Proud warriors devoted to His holiness, they served with unwavering loyalty.
The lust for aerial combat was in their blood from birth and the chapter proved themselves time and again to be masters of dramatic entry and strapping a jetpack onto absolutely every conceivable thing. Because come on, frikkin' jetpacks.
Among them, there was one name known not only to a select few. Not just another random scribble within the endless archives of the Imperium. A man of exceptional willpower who possessed perhaps the rarest trait in the galaxy. Common sense.
Captain Marcus Drachen, devoted servant of the Emperor. Sworn defender of the Imperium and humanity as a whole. And, from his point of view, one of the few rational beings in the galaxy.