Adeptus Custodes - The Firstborn: The origins of the Custodian Guard are shrouded in myth and legend. The ancient Legio Custodes were the bodyguards and sworn protectors of the Emperor and His chosen emissaries, and when the need arose, His most deadly executioners. Genetically engineered male and female warriors of unswerving loyalty and unshakable purpose, their might and skill-at-arms was greater even than the Space Marines of the ancient Legiones Astartes, while their weapons and wargear were uniquely potent, representing the apex of the Imperium's technology. Their history is a long one, and for centuries they have walked in the Emperor's shadow as His praetorians and the protector of His secrets.The Legio Custodes are by many accounts the Emperor's true firstborn, prefiguring even the gene-crafted Thunder Warriors of the Unification Wars. They are His first genetically-engineered, psycho-indoctrinated warriors, perfected weapons crafted by the Emperor's genius from the dread lore of the Dark Age of Technology.They are in almost every measurable way superhuman: stronger, faster, more acute of senses and more resilient than even the doomed Thunder Warriors or the Space Marines who would follow them, and so far beyond the limits of an unaugmented Human as to be almost godlike in comparison. Indeed, only the primarchs and above them the Emperor Himself exceeds them in corporeal might, and to meet them in open conflict is to court death for Human or alien alike.They are rare creatures, these firstborn of the Emperor's gene-craft. Such was their psycho-physical design, and the intricacy and sophistication of the gene-craft involved, that the modifications which went into their creation required such strict biological and psychological criteria that only a mere one in many thousands of potential candidates might prove suitable for the simplest of the steps involved in the Legio Custodes creation process.Even of this small pool of candidates, survival through the multiple solar decades of alchemical augmentation and psycho-memetic training were far from guaranteed. In this fact can be seen a pattern also replicated in the Space Marine Legions, only to a far greater degree. While the numbers of the Legiones Astartes were prevented from growing beyond perhaps a million at their greatest strength by the temporal and biological limitations inherent in the means of their creation -- a paltry sum compared to the billions of others who took part in the Great Crusade -- the Legio Custodes could never have operated on the scale of the Space Marine Legions, even if the attempt had been made.As a result of the inherent difficulty of their creation, the number of active Legio Custodes warriors never, it is believed, exceeded 10,000. This figure was first attained towards the middle stages of the Great Crusade and maintained diligently enough that the "Ten Thousand" itself became a cognomen for the Custodian Guard in the works of the Remembrancers and the notaries of the Imperial Court since, whatever its literal accuracy.Certainly no more than a thousand have ever been seen together at any one time, and then only once at the famous Battle of Gyros-Thravian, fought during the Great Crusade against the Ork Warlord Gharkhul Blackfang and his vast Greenskin horde. The primarchs Horus, Rogal Dorn and Mortarion and their Legions were vastly outnumbered and close to defeat when the Emperor led an assault from His golden battle barge, the Bucephelus. At the head of a thousand Custodians, the Emperor struck at the very heart of the Ork horde, confronting Gharkhul atop a towering Gargant.As the Emperor decapitated the giant, black-skinned Ork, the Custodians laid waste to the warlord's prime warriors. It is said that within moments over a hundred thousand Greenskins died and the WAAAGH! was broken. Legend has it that only three Custodians fell at the battle, their names enshrined forever and engraved on the Emperor's armour thereafter.