The Knights of Thunder is a Loyalist Space Marine Chapter comprised entirely of Primaris Space Marines, created from an unknown lineage and raised during the Ultima Founding of ca. 999.M41. These supreme transhuman warriors were created by order of Roboute Guilliman, the recently resurrected Primarch of the Ultramarines, who had tasked Archmagos Dominus Belisarius Cawl with crafting a legion of new genetically-enhanced warriors to serve as Humanity's last line of defence following the Horus Heresy.
Even then, Guilliman foresaw a time of encroaching darkness when Chaos would threaten the galaxy itself. These gene-crafted warriors are intended to protect the Imperium of Man against Chaos, xenos and the myriad threats that close in upon Mankind from all sides. They are the key components of the resurrected Primarch's Indomitus Crusade to reclaim the galaxy.
The Knights of Thunder fought as part of the Indomitus Crusade and the Chapter's name has been inscribed in glory on victory monuments raised across the Imperium recognising their contribution to those heroic campaigns to stablise the Imperium in the wake of the Great Rift's birth.
For ten millennia, Archmagos Dominus Belisarius Cawl has been working on a task set for him by the Primarch Roboute Guilliman before he was mortally wounded by the Daemon Primarch Fulgrim in the days after the Horus Heresy: a new legion of transhuman warriors. Developed on orders from Guilliman 100 standard centuries past, Primaris Space Marines were diligently developed and perfected by the Priesthood of Mars during the long intervening millennia. As an optimist, but never a fool, Guilliman learned from the mistakes of the Horus Heresy, and he foresaw that the Forces of Chaos would never relent in their aim to bring the Imperium low. He anticipated that devastating times would once again engulf the galaxy and knew that warriors resilient enough to stand against them would be needed as never before. That time has surely come. Now, as the Imperium of Man is poised on the brink of annihilation at the hands of Chaos, his task is at last complete.
The Primaris Space Marine is a new breed of hero for this, the darkest age in the Imperium's history. These new warriors are the next step in the evolution of the Emperor's Angels of Death -- genetically altered from their brethren to be bigger, stronger and faster -- timely reinforcements for the Imperium's armies as their enemies close in for the kill in the wake of Abaddon the Despoiler's 13th Black Crusade and the birth of the Great Rift dividing the Imperium in two.
At the dawn of the Indomitus Crusade to retake the Imperium from the advancing armies of Chaos and xenos alike, Lord Commander of the Imperium Roboute Guilliman has gathered his new armada, along with elements of the Adeptus Custodes, a small contingent of the Silent Sisterhood. They were not alone. Upon nearby Mars, Archmagos Dominus Belisarius Cawl had unlocked his vaults, producing from stasis the fruits of his longest labours -- the Ultima Founding. To complete the full deployment of his long-prepared masterworks would take months. Cawl's own fleet joined the Primarch, headed by his freighter-hulk, Zar-Quaesitor, a mech-ark class ship that carried within its massive hull a vast number of Primaris Marines still in stasis hibernation. The Archmagos brought with him several armies of Skitarii and Legio Cybernetica, alongside three lances of Questoris Knights from House Taranis.
As the Indomitus Crusade penetrated deeper into the galaxy, thousands of hibernating Primaris Space Marines -- some comprising entirely new Chapters and others designated as reinforcements for existing ones -- were awakened from their millennia-long slumber and made ready to join the fray. Many Chapter Masters welcomed their Primaris brethren into their ranks, accepting the new reinforcements gladly. Others, though, viewed these new creations with suspicion or outright hostility, claiming that the Emperor's work should never have been meddled with by mere mortals.
The Knights of Thunder's Chapter colours are currently unknown in Imperial records.
The Knights of Thunder's Chapter badge is not currently listed in Imperial records.
- Codex Adeptus Astartes - Blood Angels (8th Edition), pg. 42