Thunder Warriors - Flaws: Despite their many early victories in the Unification Wars, the Thunder Warriors were far from perfect. Some were mentally unstable, others suffered catastrophic biological and metabolic failure unpredictably after a span of standard years, their own superhuman physiques turning against them in the end.It seems obvious in retrospect that the Emperor knew early on that the nascent Imperium needed a more permanent and stable force of gene-enhanced warriors, so even while the Thunder Warriors waged war in the Emperor's name, He gathered about Him a team of savants and gene-wrights, some willing and others as captives taken from his foes, and constructed new genetics laboratories deep in the vast dungeons of his Terran fortress in the Himalazian (Himalayan) Mountains. This team became known as the Imperial Biotechnical Division.The labour there went on for solar decades in absolute secrecy and resulted in the creation of the primarchs and many other wonders of the Emperor's arcane and unmatched gene-craft, known and unknown. Yet the foremost of these creations were the twenty Space Marine Legions, the Legiones Astartes of legend.Into their creation went all the secret history and genetic lore of the Age of Strife, hard wisdom gained through the success and failure of the Thunder Warriors who were the Space Marines' prototypes and the fruits of the Emperor's own inimitable genius.The first among the Space Marines were hand-picked men from the Emperor's personal, mortal bodyguard. These volunteers were subjected to surgical, genetic and psychological modification. With rigorous training and appropriate mental conditioning they became not only immensely strong and tough, but iron-willed and disciplined, an unstoppable force whose loyalty to the Emperor was unflinching.Quickly the process was refined and systematised, and the numbers of the new genetically-enhanced warriors, at first armed and armoured as the Thunder Warriors had been, grew swiftly. They were organised into twenty distinct regiments numbering at first no more than a few hundred warriors each, much like the superhuman soldiers they were to replace.Although it remained a dire secret at the time, it is now widely believed that this division was more than a merely administrative one, as each regiment contained variant "gene-seed" encoding drawn from a different primogenitor primarch.This often manifested its influence in subtle and unexpected ways, not least of all in influencing and altering the psychological character of the genetically enhanced warrior. With the Astartes regiments expanding rapidly into legions with the intake of new blood from the areas of Terra that had already joined cause with the Emperor, the new warriors quickly eclipsed and replaced the mighty but far less disciplined and unstable Thunder Warriors. With the Space Marines at the forefront of Imperial efforts, victory followed victory in quick succession.Though the Thunder Warriors were superior in every physical aspect of their creation to the later Space Marines, they suffered from one flaw the later Astartes would not -- their lifespans were extremely short. The Thunder Warriors were not created to live beyond the achievement of Unity.This was a genetic flaw that may have been deliberately written into their DNA during their creation to assure that when their usefulness was at an end, these warriors would cease to exist so that they might be replaced by the more balanced transhuman warriors of the Legiones Astartes. The Thunder Warriors were created to be a broadsword rather than a scalpel like the Astartes who would come after them.Unlike most Space Marines, the Thunder Warriors were cold-blooded, ruthless killers who enjoyed the savagery and feeling of power they experienced during combat and possessed talents for nothing other than war. In many ways they represented the worst aspects of Humanity's nature rather than its best. As the Unification Wars drew to a close, the Emperor knew that He would still need the superior skills of gene-modified warriors in order to carry on His "Great Crusade" and conquer the galaxy.It was for this reason that He had moved to craft the genetically-engineered warriors who were truly superior in every way to average Humans -- morally, spiritually and intellectually as well as physically. These perfections of the transhuman warrior template would become the first true Space Marines of the Legiones Astartes. The Thunder Warriors were discarded as imperfect tools that had served their purpose.The present-day members of the Adeptus Astartes are not the ancient Thunder Warriors' equals in the realm of pure combat. Yet, though the Thunder Warriors were stronger, hardier and more resilient than the later Astartes, their genetic legacy was never meant to last beyond the achievement of Terra's Unity.The proto-Astartes were a means to an end, the conquest of a single world, whilst their genetic successors were intended to travel to the stars and conquer a galaxy. The Space Marines were also to serve as living embodiments of all that Humanity could hope to achieve.It is the great tragedy of the Imperium that while the Space Marines were created to represent the pinnacle of Human development, they ultimately proved as susceptible to the basic flaws of Mankind as any other mortal.