Abaddon - Great Crusade: By the time of the Great Crusade, Ezekyle Abaddon had been recognised as the greatest warrior of the vaunted XVIth Legion after their Primarch Horus. He was blessed with being able to serve at the right hand of the Primarch himself, for to witness such a being in the flesh was to be in the presence of a demigod. Abbadon was the first and most respected of them all, a man who worshipped his Primarch as a god, just as Horus worshipped his father the Emperor of Mankind in turn.Horus Lupercal was raised up by the Emperor Himself as the greatest of all the Primarchs' number, an accolade never surpassed before or since. Yet amongst Horus' many virtues was his humility. He listened well to the counsel of his warriors, learned from his mistakes, and considered every action before committing to it.Amongst his advisers in the Luna Wolves, he trusted four officers above all. This council of warrior captains was known as the Mournival. At the time of the Horus Heresy's beginnings it was comprised of Abaddon himself, Tarik Torgaddon, Captain of the 2nd Company, Horus "Little Horus" Aximand, Captain of the 5th Company and Garviel Loken, Captain of the 10th Company.It was after the battle for the world designated Sixty-Three Nineteen by the XVI Legion, in which Tenth Captain Garviel Loken managed to reach and slay the impostor Emperor who ruled the world ahead of Abaddon, that the First Captain recommended Loken's elevation into the Mournival to replace the 4th Company's Captain Hastur Sejanus. Sejanus, a particular favorite of Horus, had been slain shortly before the battle.As the Great Crusade conquered its way across the stars, it reunited many of the scattered domains of Mankind that had been abandoned and isolated by the chaotic tides of the Warp. Always at the fore was Horus Lupercal, with Abaddon at his side. They were the first into battle, the first to exhort their brother Legions to acts of greatness, and the first to encounter the strange new threats that had grown in the dark corners of the galaxy.One of these threats was a danger so insidious that it slowly corrupted many of the Legiones Astartes, including the Primarch Horus himself. Abaddon was also a member of the Legion's Warrior Lodge, the "quiet order" within the Luna Wolves, inspired by similar lodges on the Feral World of Davin -- which the Luna Wolves had brought to Imperial Compliance many years earlier.Erebus, first amongst the Chaplains of the Word Bearers Legion and first amongst the worshippers of the Chaos Gods, had spread his secret warrior lodges to the brethren of the Luna Wolves as well as many of the other Space Marine Legions at the behest of his corrupted Primarch Lorgar in the decades before the Heresy began. In the daylight hours, those of the Legiones Astartes who had secretly come to worship Chaos used their twisted logics to sway more of their number to their cause.During one particular Imperial Compliance action, Abaddon notably stood against Horus' attempts to negotiate with a stray branch of humanity known as the Interex, preferring to adhere to the Emperor's stated policy, and simply demand surrender or force Imperial Compliance upon newly discovered human cultures. This attitude was reversed in desperation after Horus was critically injured by the Chaos-corrupted Imperial Planetary Governor Eugen Temba upon the XVI Legion's return to the world of Davin.Horus was mortally wounded after slaying the Nurgle-corrupted Temba upon the bridge of his downed starship on Davin's moon, which had been transformed by Nurgle's corruption into a reeking swamp infested with undead Plague Zombies, Temba's own former Imperial Army garrison. Temba had wielded a blade dedicated to Nurgle known as the Kinebrach Anathame that had infected the Primarch with a toxin so virulent that even a Primarch's superhuman immune system and all the advanced technologies of his Legion's Apothecaries could not defeat it.Blinded by grief, Abaddon and his fellow company captains took the Primarch's body on the advice of the Word Bearers' First Chaplain Erebus to a mystic healer who belonged to the Chaos Temple of the Serpent Lodge on Davin and who was actually a Chaos Sorcerer -- an act in utter contradiction of the Imperial Truth (which was stridently atheistic) and which opened Horus up to the influence of the Ruinous Powers of Chaos.Yet instead of salvation, the priests of that Davinite moon brought eternal damnation. When Horus emerged, a change had been wrought in him, and a shadow lurked behind his eyes that would never leave. The seed of bitterness that had been planted in Horus’ heart ultimately blossomed into a fullscale heresy that nearly tore the Imperium apart.