Unification Wars - Thunder Warriors: During this time the Emperor created a number of military organisations, such as the Imperial Army, which would become the nucleus of the armed forces that would support his Legiones Astartes and his reconquest of the Human-settled galaxy.Amongst the early units that saw action during the Unification Wars were such venerable regiments as the Geno Five-Two Chiliad, which would become one of the oldest and most respected regiments within the later Imperial Army alongside similar veteran units remembered as the "Old Hundred." Like many of these early regiments, the geno-soldiers were created through the use of some of the Emperor's sophisticated genetic engineering techniques, developed in His laboratories beneath the Himalazian (Himalayan) Mountains and among the Selenar gene-wrights on Luna.The most elite of this first generation of genetically-engineered supersoldiers were known as the Thunder Warriors, the Legio Cataegis in High Gothic, men who were physically stronger and more formidable in combat than even the later Space Marines, though they were engineered to be vicious killers and lacked many of the more noble aspects of the later Astartes as well as their tremendously long lifespans. The Thunder Warriors were engineered to be the means to an end and were never intended to be integrated into the Emperor's new realm after Unity had been achieved.Through genetic engineering and selection the standard geno-soldiers displayed many of the characteristics of the perfect Human warrior -- they were physically more resilient, stronger and capable of taking more damage than any of their unaltered techno-barbarian foes. These early genetically-engineered Imperial Army regiments would go on to continue serving the Emperor after the conclusion of the Unification Wars.These regiments would eventually be referred to as the "Old Hundred," and would form the core of the initial military force that embarked upon the Emperor's galaxy-spanning Great Crusade in ca. 798.M30 beside His newly-created Space Marine Legions.The Emperor accepted the deaths of the many innocents that resulted from the conquest of Terra with great remorse in order to achieve the greater good of unifying Humanity and protecting it from the manifest predations of the Warp and predatory xenos of the galaxy.Unimaginably large, full-scale battles during the Unity campaign would last for solar weeks on end, with body counts in the millions that sundered mountains and split entire continents. Future Imperial scholars would later dismiss these victories as lurid hyperbole, refusing to believe that such clashes of arms could possibly have been fought, but indeed they were.The Imperial historical chronicles tell of the last battle of the Unification Wars, known as the Battle of Mount Ararat, which was fought in the Kingdom of Urartu. During this final battle the remaining Thunder Warriors were slain to a man. The chronicles recorded that the famed Thunder Warrior Arik Taranis, known as the "Lightning Bearer," raised the Banner of Lightning at the final declaration of Unity which established the rule of the Emperor of Mankind over the entirety of Terra before dying of his wounds. It was a measure of the Thunder Warriors' heroic sacrifice that they had all died to win the last and greatest victory for the Emperor.Unfortunately, this heroic version of events was completely false. The Thunder Warriors had not died to a man during the final battle of the Unification Wars. They had been brutally culled from existence by the Emperor's own servants on His orders. The Thunder Warriors had been betrayed by their own creator, a terrible secret skillfully concealed from the people of the Imperium for more than 10,000 Terran years.But there were reasons for this betrayal. The Thunder Warriors were not like the Astartes who would follow them; they had been created solely for war and were not well-suited to any other activities. Once peace came to Terra, the Thunder Warriors would inevitably pose a risk to the new state's stability through their very existence and the flaws that had resulted in much mental instability and early deaths due to metabolic collapse among their ranks.The Thunder Warriors had been enhanced as mature, adult men and their bodies often rebelled against the genetic changes only a few short Terran decades after the transformation. All this meant that the Thunder Warriors could not be allowed to survive the conflict they had been created to fight.At first the Emperor simply did not replace their numbers as they fell to battle or insanity, but then decided to take more active measures. According to Arik Taranis, the final culling of the Thunder Warriors took place following the victory of the last battle of Unity, and was carried out by the Legio Custodes, the only soldiers in the Imperial armies capable of defeating the Thunder Legion.Another source claims that even before the Unification Wars had ended, the Thunder Warriors at last realised that their creator had cursed them with short lifespans as a result of their imperfect genetic augmentations, and turned upon Him for what they saw as His betrayal. It was a cadre of several hundred Custodians, even then believed to have been led by the legendary Constantin Valdor, and accompanied by several thousand prototype Astartes of the Ist Legion of the newborn Space Marines, that stood in the Emperor's defence, carrying out a merciless culling of the obsolete and rebellious gene-soldiers.Though some Thunder Warriors successfully escaped the cull, however it happened, the vast majority of those who survived the Unification Wars died at the hands of their own allies.