Lorgar

Lorgar was the prophet among the primarchs, a being of towering faith recovered on the temple-world of Colchis, where he had already overturned an entire religious order through the sheer power of his conviction and his words. Of all the Emperor's sons he was the least suited to a purely material crusade, for his soul hungered for the divine, and he poured that hunger into the worship of his father, building the Word Bearers into a Legion of missionaries who conquered through faith as much as through force.

The Emperor's rejection broke something in him. When Monarchia was razed and Lorgar made to kneel in its ashes, forbidden to worship the one being he believed truly worthy of it, his devotion did not die but turned. If the Emperor would not be his god, then the Urizen would find gods who would, and his long pilgrimage into the darkness led him to the four powers of Chaos and the revelation he named the Primordial Truth. Everything that followed flowed from that wound. Patient, certain, and utterly convinced of his own righteousness, Lorgar set out to remake the galaxy in the image of true faith, and became the quiet architect of the greatest betrayal in human history, the first primarch to fall and the one who drew all the others down with him.