Leman Russ - The Wolf King and the Burning of Prospero: In stark contrast to the feral and barbaric Space Wolves, the Thousand Sons Legion was fixated on the pursuit of lore and knowledge, particulalrly concerning the Warp and psychic sorcery. Their Primarch Magnus the Red possessed copper-skin, fiery hair and most striking of all, a single eye after the other was lost to his continued dabbling in sorcery. Magnus' strength was lauded as rivaling that of even Russ, but he preferred to expend his energies learning and pursuing ancient arcana than the arts of battle. His physical peculiarities were never remarked upon by the other Primarchs; after all, many of them bore some sort of physical peculiarity or another. Nonetheless, the Wolf King feared his brother's pursuit of sorcery, believing it to be inherently wicked and dishonourable. But the Emperor refused to hear Russ' suspicions, as Magnus was one of his own sons and the Emperor Himself was the mightiest psyker ever known to Mankind.As the events leading up to the Horus Heresy ripened into terrible fruition, Magnus the Red sent a psychic message to the Emperor, warning him that Horus had been corrupted by the Ruinous Powers. But for the message to reach his father, it had to be powerful enough to disrupt the psychic wards that had been erected to surround the Imperial Palace, where the Emperor had been engaged in a highly secret project in the palace's lowest levels to open up the Eldar Webway to the use of Mankind. The disruption of the Emperor's wards allowed the malevolent entities of Chaos to penetrate into the Webway and put Terra itself at risk of a Chaotic assault. Greatly angered that Magnus had disregarded the Council of Nikaea's ruling that had made the use of sorcery illegal within the Imperium, the Emperor chose to believe that it was Magnus, not his beloved Horus, who had been corrupted by the Chaos Gods and was only seeking to make trouble for his brother.The Thousand Sons had continued their practice of sorcery despite the Emperor's decree specifically forbidding it. Their guilt revealed, the Emperor saw no other choice but to send Leman Russ to the Thousand Sons' Legion homeworld of Prospero and bring back Magnus the Red with him to Terra to account for his actions and his violation of Imperial law. The Emperor believed Magnus and his Legion to be the true traitors and Russ was all too easily convinced likewise because of his own longstanding prejudice against sorcery and Magnus' unhealthy fascination with it. But once he and his Legion were in transit towards Prospero Horus "convinced" Russ of Magnus' treachery, and drove Russ into a furious rage against his brother. He further convinced the Wolf King that the Emperor had changed his orders and he wanted the Space Wolves and their accompanying forces from the Sisters of Silence and the Imperial Army to launch a full-scale planetary assault on Prospero to wipe out the Thousand Sons and slay Magnus before he could turn upon the Imperium. Horus' evil gambit proved all-too-successful and Prospero was assaulted and bombarded, killing thousands within days, its great city of Tizca, the City of Light, reduced to a shattered landscape of blazing pyramids. Ultimately, for all their wisdom, the Thousand Sons could not stand against the fury of the entire Space Wolves Legion and their Imperial allies on the field of war.In the final titanic battle between Leman Russ and Magnus the Red, the sorcerous Primarch used sorcery to make himself stronger so that he could survive the Wolf King's assault. Enraged by this blatantly dishonourable trick, Russ gathered his strength and raised Magnus over his head and broke his brother's back over his knee. Summoning a Warp rift after calling out for aid to the Chaos God Tzeentch, the Changer of Ways, Magnus and his surviving Thousand Sons then escaped into the Warp, where they would swear vengeance upon the Emperor and the Imperium that had treated them so unjustly and brought down the pyramids of fabled Tizca. The grudge between the Space Wolves and the Thousand Sons would last for millennia, though the Space Wolves would be engaged far from Terra and would play no other major role during the most important battles of the Heresy.