Oll Persson is from the wayback when I first started playing (2nd Ed), he used to appear as a Saint on Imperial Guard banners where the description was that "He sacrificed himself to save the Emperor during the siege of Terra"
As to it being a Custodian who got flayed by Horus's gaze, in the original story it was an astartes Terminator.
"For a second the Emperor knows only darkness then a flare of agony brings him back to consciousness as Horus rips his arm from its socket. The Warmaster howls with bestial triumph.
Suddenly the battering stops. Through his good eye the Emperor sees a solitary Terminator has entered the room. The Marine charges towards the Warmaster, stormbolter blazing. Horus looks at him and laughs. For a moment he stands triumphant, allowing the Marine to see what he has done to his Emperor.
The Emperor knows what is going to happen next, sees the gloating triumph on Horus' face. There is no trace of his friend left there. There is only a daemon driven by insane destructive fury.
Horus turns his burning gaze on the Terminator and the Marine's flesh flakes away to reveal his skeleton, then even that is gone, reduced to dust.
The Emperor sees the trap that has been set for him. He has been restraining himself, trying not to hurt one who had been as a son to him. Now he sees that there is no trace of his trusted comrade left. He knows that he must stop this semblance of his former friend and avenge the fallen Terminator. He must strike one deadly blow. He will get no other chance.
He gathers every particle of his power, focuses it into a mighty bolt of pure force, more coherent than a laser, more destructive than an exploding sun. He aims it as Horus, a lance of power destined for the madman's heart. Horus senses the upsurge of energy and turns to face the Emperor, a look of horror on his face.
The Emperor lets fly. It strikes the Warmaster. Horus screams as destruction rains down on him, twisting and writhing in titanic agony. He strives frantically to counter the Emperor's deathblow but his struggles become more feeble as the lethal energies play over him.
Driven by all the force of his rage and pain and hatred the Emperor wills Horus's death. He senses the forces of Chaos retreat, disengaging themselves from their pawn. As they do so sanity returns to the Warmaster. The Emperor sees realisation of the atrocities he has committed flicker across Horus' face. Tears glisten there.
Horus is free but the Emperor knows he himself is dying and that the Powers of Chaos may once again possess the Warmaster and he will not be there to stop them. He cannot take that risk. Horus must die. Yet for a second, looking into his old friends face, he hesitates, unable to do the deed. Then he thinks of the slaughter that still goes on outside, may go on forever. Resolve hardens within him.
He forces all mercy and compassion from his mind, empties it of all knowledge of friendship and coimraderie and love. His eyes lock with Horus and see understanding there. Then with full cold knowledge of what he is doing the Emperor destroys the Warmaster.
Rogal Dorn enters the chamber. Horror fills him as he sees the mutilated form of the Emperor and the shrivelled husk inside the Warmaster's armour. He curses himself for taking so long to fight through the Chaotic hordes, He knows now why their attacks ceased and why the ship is reverting to normal.
He rushes to the Emperor's side, detecting the faint pulse of life. Perhaps there is yet hope. Perhaps the ruler of the Imperium may live.
Rogal Dorn will do his best to ensure it. "
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