The Word Bearers are one of the nine First Founding Space Marine Legions that betrayed the Emperor of Mankind during the Horus Heresy.
At present, the Word Bearers' greatest foes amongst the servants of the Emperor are the Ultramarines and their Successor Chapters, who the Word Bearers have hated and seen as rivals since the time of the Great Crusade.
The Word Bearers are the scions of the Primarch Lorgar, the Dark Apostle of Chaos and first of the Primarchs to be corrupted by the Ruinous Powers.
The priests of this primitive faith preached that one day, a supreme being would come to lead them into a new age.
Lorgar was raised within the Covenant's greatest temple, learning all its secret rites and texts and compiling a vast body of his own wisdom that came to be known as "the Word." When the Emperor finally came to Colchis, the Primarch saw in the Master of Humanity the being spoken of in the ancient Colchisian prophecy.
Thus were sown the seeds of the Heresy, and Lorgar determined that in order to avoid the fate that the weakling Eldar had brought upon themselves at the moment of the creation of the Eye of Terror and the birth of Slaanesh, Humanity must embrace Chaos in all its glory.
Only then, Lorgar knew, would Humanity ascend to the pinnacle of existence in a universe reshaped in the boundless image of the Warp.Possessed of this new knowledge, Lorgar returned to the Great Crusade.Where previously the Word Bearers had been criticised for their slow progress, enforced by their drive to cast down primitive idols and replace them with those of the Emperor, now their rate of conquest was prodigious.In the Ruinous Powers, Lorgar found such beings, and the truth was revealed to him.The Emperor had been truthful when He had stated that He was no god, but Lorgar saw that the Master of Mankind had told the very worst of lies when He claimed that no such beings existed.In so doing, the Word Bearers tied up the single biggest Legion at a time when it was most needed.