Fulgrim

Fulgrim rose from the dying world of Chemos, where as a foundling he drove back the machines' decay and lifted an entire civilisation from the brink through sheer, relentless will. When the Emperor united him with the III Legion, he gave his sons the creed that had saved his homeworld: that perfection, pursued without compromise, could conquer any darkness. For a time he seemed its living proof, a primarch of dazzling charisma and flawless accomplishment, beloved among his brothers and admired above nearly all.

Yet the road to perfection had no end, and on the world of the Laer, Fulgrim took up a daemon-blade that whispered to the emptiness his endless striving had opened within him. The serpent's poison worked slowly, dressing corruption in the guise of ambition, until the Phoenician gave himself to Slaanesh without ever quite realising he had fallen. At Isstvan V he cut down Ferrus Manus, the brother he had loved most, and in that moment sealed both his treachery and his damnation. What emerged from the Heresy was no longer the paragon the Emperor had raised, but a creature of exquisite cruelty who had traded a father's dream for a god's applause.