Thunder Warriors were the elite super-soldiers that marched with the [[Emperor]] to conquer [[Terra]] in the [[Wars of Unification]]. The engineering that the Emperor used to create the Thunder Warriors, whilst creating superior fighters, was not as efficient as what was used later to create the [[Space Marine]]s{{Fn|3}}, nor was the technology as advanced or the geneticists as entirely willing.{{Fn|5a}} These proto-Astartes were organized organised into twenty regiments of no more than a few hundred warriors, each named by the Emperor himself.{{Fn|4b}}

===OrganizationOrganisation===Like the later [[Legiones Astartes]], the Thunder Warriors were organized organised into twenty Legions, each led by a [[Primarch]]. However, unlike the Astartes Primarchs, Thunder Warriors Primarchs were not physically different from the warriors they led. Instead, they were simply superlative warriors who were promoted to the position by the Emperor.{{Fn|10a}}

The Legions of Thunder Warriors seem to match that of the Astartes. For instance, the 4th Legion of Thunder Warriors was known as the ''Iron Lords'' and specialized specialised in siegecraft. This closely resembles the subsequent [[Iron Warriors]].{{Fn|10a}}

Thunder Warriors were large, greater in size than most [[Space Marine]]s. In their earliest days the Thunder Warriors wore metal armor armour with leather strappings and wielded [[Lasgun|Lasrifle]]s.{{Fn|10a}} Despite physical deterioration, the few Warriors that survived the end of the [[Unification Wars]] were easily more than a match for an Astartes. Even severely deteriorated Thunder Warriors were capable of fighting multiple Astartes at once.{{Fn|5b}}{{Fn|8}} They were made highly resistant to psychic attack, perhaps because of the sorcery they would regularly face during the [[Age of Strife]], with any attempts at mental attack causing severe pain to the psyker.{{Fn|8}} They had tremendous upper body strength that was considered to be unparalleled, which when coupled with their early model of [[Power ArmorArmour#Mark_1_.22Thunder_Armour.22|power armorarmour]], made them virtually unbeatable in close combat.{{Fn|2}}{{Fn|5b}}{{Fn|8}} The leg strength of even a heavily physically deteriorating Thunder Warrior made them capable of kicking completely through the torso of a normal human.{{Fn|8}} Their bones were thicker than that of an Astartes, with a Thunder Warrior capable of shattering the skull of an Astartes with a headbutt.{{Fn|2}} Their reflexes were also extremely enhanced, allowing a Thunder Warrior to dodge the shot from a plasma gun, while already engaged in and focusing on fighting two other Astartes.{{Fn|8}}

The Thunder Warriors genetic template was unstable and they were prone to fits of bloodlust and instability. Short-lived and rife with both mental and physical health issues, Thunder Warriors were known to suddenly drop dead or stop following orders.{{Fn|10a}} Unlike the later Legiones Astartes, they lived as warlords and relished battle. Their human emotions were not expunged from them, and they were known for their dry humorhumour.{{Fn|10b}}

Four Thunder Warriors had also survived on Terra to serve as gladiators in depths of The Maw, near slums known as the Swathe, for despite their physical deterioration they were still mighty warriors. They had been kept alive by '''Tarrigata''', a former [[astropath]], who served as their master and helped keep them alive through transplanting the organs of the deceased Thunder Warriors. One of them (Kabe) eventually died after being incapacitated in a gladiator battle against a [[Chrono Gladiator]], before being ceremonially executed by a fellow Thunder Warrior. Another (Gairok) became mentally unstable and was slain when he attacked one of the other Thunder Warriors. The third (Vezulah Vult) died fighting a demonically [[Possessed Marine|possessed]] [[Alpha Legion]] warrior, after being blinded by the AstarteAstartes's acidic spit and eviscerated. The last (Dahren Heruk) was given an honoured death by a Custodian, after he defeated the possessed legionary and saved the Custodian's life.{{Fn|8}}

It is possible that the World Eater and later [[Blackshields|Blackshield]] [[Endryd Haar]] was a Thunder Warrior or another kind of proto-Astartes who was successfully transformed into a Space Marine. He was far larger, stronger, and quicker than other Space Marines; furthermore, he was extremely brutal and somewhat mentally somewhat unstable despite lacking the [[Butcher's Nails]]. Malcador singled him out as a special case. Haar himself confirmed that he had fought alongside the Emperor in the Unification Wars and called the Dait'Tar "brothers".{{Fn|14}}{{Fn|15}}{{Fn|16}}