Kor Phaeron
Kor Phaeron is the First Captain of the Word Bearers and Keeper of the Dark Faith. On Colchis, he was a priest in the Covenant, and the one primarily responsible for raising Lorgar. When young Lorgar began having hallucinations about a messiah coming to Colchis, members of the Covenant tried to have him killed, and Lorgar lead a civil war against the Old Faith. Phaeron sided with Lorgar, more out of loyalty to his foster son than any religious conviction. After six years, Lorgar's forces won, and shortly afterwards, the Emperor arrived on Colchis, and made Lorgar commander of the XVIIth Space Marine Legion, which Lorgar renamed the Word Bearers. Kor Phaeron wanted to join Lorgar in his new crusade, but since he was already an old man by this point, could not become a proper Space Marine. So they gave Phaeron some of the organs, along with a ton of juvenant treatments, and he was appointed Captain of the First Company. Half the Legion in turn hated Phaeron for the nepotisim and the fact that he was not a true Astartes, while the other respected his skills as a preacher. Regardless, Phaeron's transformation makes his relationship with Lorgar even more complicated, as Lorgar is Phaeron's foster son, but Phaeron was turned into Lorgar's gene-son. Confused yet?
When the Emperor rebuked Lorgar for spreading the Cult of the Lectitio Divinatus, Kor Phaeron, along with First Chaplain Erebus, was the one who told Lorgar that if the Emperor was unwilling to embrace worship, there might be other gods who would welcome it, leading Lorgar down the path to Chaos. During the Horus Heresy, Kor Phaeron lead the Word Bearers assault on Calth, in revenge for the Ultramarines role in Lorgar's rebuke. Having Roboute Guilliman at his mercy, Kor Phaeron decided to try and turn Guilliman to Chaos. This was a mistake, as Guilliman was able to rip out Kor Phaeron's primary heart. Running back to his battle barge, Kor Phaeron ran like a bitch to the Maelstorm, eventually making his way to the Word Bearers new homeworld of Sicarus. Currently, Kor Phaeron and Erebus are the co-leaders of the Word Bearers in Lorgar's absence.