Dark Angels - Great Betrayal: In the aftermath of the Siege of Terra, the surviving Loyalists rallied the reeling Imperium. The Dark Angels took a significant part in these battles, which later came to be called the Great Scouring.As they pursued the rebels, the Ist Legion diverted to nearby Caliban for the first time in many standard years, since the world had been enshrouded by the Ruinstorm and other Warp storms since Horus' betrayal but now was free of such navigational interference.For Lion El'Jonson, one final act of treachery remained to be discovered. Upon the Dark Angels' arrival in orbit, they were fired upon from the surface. Pulling back the Legion fleet, El'Jonson tried to find out what had happened, and discovered that Luther -- who had become embittered by what he perceived as El'Jonson always taking all the glory -- had poisoned the minds of the Dark Angels garrison and the new recruits that had been left on the planet against their primarch.Correctly believing that Luther and the planet-side Dark Angels had actually been tainted by Chaos, an infuriated Jonson ordered that Caliban be bombarded from orbit, destroying the planet's defences.El'Jonson then led his forces to the surface and assaulted The Order's fortress-monastery, where he confronted Luther in single combat. Luther, now a Chaos Champion, had been elevated to a strength equal to that of the primarch through the "gifts" of the Chaos Gods and the two met in a combat the likes of which would not be seen again. The pair's duel levelled the monastery around them but the planet was also taking a heavy toll. The sustained bombardment began to crack the surface of the planet's crust, the Dark Angels in orbit unable to see the damage they were wreaking upon their homeworld. El'Jonson managed to wound Luther, but could not bring himself to kill the man who had once been his brother and mentor.Luther lashed out with a powerful sorcerous attack that mortally wounded the primarch. Luther then realised what he had done in his jealousy and anger, as if a veil of deceit had suddenly been lifted from in front of his eyes. He fell to the floor, unwilling to fight any more, but it was too late for El'Jonson. The enraged Ruinous Powers of Chaos realised they had lost control of yet another of their pawns in the fight against the Emperor, and sent a massive Warp storm to wrack the surface of the planet. Caliban then broke apart under the strain, destroyed all but for the monastery of The Order which had been protected by potent defensive force fields.The rest of the Dark Angels who had been converted by Luther to the worship of Chaos were sucked into the Warp and scattered across the galaxy. From that time forward they were named the "Fallen Angels" or simply "the Fallen." The Fallen were scattered throughout space and time, and Caliban tore itself apart under the strain of the Ruinous Powers' assault.When the Dark Angels descended to what remained of Caliban, now little more than an asteroid upon which stood The Order's fortress-monastery, they searched the ruins and found Luther mumbling that El'Jonson had been taken by the Watchers in the Dark and would return one day and forgive Luther for his sins. The Dark Angels could not find any trace of their primarch.The truth was that the Lion still lived, though he had been placed into a coma and had reemerged into realspace with the aid of the Watchers in the Dark in a secret chamber deep beneath the fortress-monastery which even his brethren did not know existed.Only the Emperor of Mankind, sitting silent on the Golden Throne from which He sees all, and the Watchers themselves, know this greatest secret of the Dark Angels. Even the Supreme Grand Master of the Chapter is not privy to this truth. However, legends soon spread throughout the Chapter that the Lion would find his way back to the Dark Angels on that grim day when they went to war in defence of the Imperium for the final time.Ten standard millennia later, a captured Fallen Angel named Merir Astelan would tell a different version of these events. According to Astelan, Lion El'Jonson was late in arriving to the defence of Terra not due to being too far away, but because he was waiting to see whether it was Horus or the Emperor who won the great conflict between them. Astelan, believing that those who were with El'Jonson would not forgive them for turning on their brothers, ordered the defensive batteries of Caliban to fire upon the returning Dark Angels' fleet.The difference between the Dark Angels' view of the fall of Caliban and that of the Fallen Angel Astelan is considered to be due to Astelan's literally warped perception of these events, but some aspects of this story may ring with truth after all, and Lion El'Jonson might have betrayed the Emperor in his heart, if not in his mind, when he was most needed.