Not quite what the previous chapter implied...

Not all of the Astartes who serve chaos are the survivors of those that fell in the Horus Heresy. While those that have died are often resurrected, and many have become Daemon Princes and cannot truly die, there are still many, even one among the very fallen Primarchs themselves, who have died permanently, their very souls consumed by demons. How then do the chaos legions remain a threat to the Imperium 10,000 years and more later?

Well, there are two ways.

1: Many Astartes from the Loyalist Chapters have turned to chaos even as the traitor legions did, sometimes entire Chapters of 1000 Battle Brothers at a time, and while most of those that turn as a Chapter stay aloof from the legions and keep their own name and colors, those who fall singly or as a squad and escape retribution tend to join up with one of the major legions.

2: There is one legendary man, Fabius Bile, who can create new Astartes with Chaos tainted gene seed, but what is not known to the Imperium is that while he is the best of and the leader of the 'Dark Apothecaries' he is far from the only one. Most legions have a few of the former apothicarion corps that turned to chaos and have learned the secrets of how to induct more marines from deals with demons and learning at Fabius knee, who replace those that succumb, ascend to Daemonhood, or are transformed into Chaos Spawn, Dreadnoughts, Havocs, or become bound into their vehicles.

Either way you are one such newly minted Traitor Marine, you do not have 10,000 years of experience under your belt, you in point of fact don't have 50 years of experience: you were chosen for induction about 30 years ago, and only 9 years ago were fully equipped and implanted as a Space Marine, either of the legions or a loyalist chapter which turned or you abandoned. You aspire to glory, to one day be a Daemon Prince and lead an army of battle brothers similar to yourself as you are now, but for the moment you must follow orders and do as you are bid, though you will of a certainty have fun along the way, though it will also of a certainty be of a hideous and corrupt nature.

Now, beginning to at last answer the preceding question, what is your name* & history**? *(As Chapter Title.) **(In Chapter Body: To which Traitor Chapter or Legion do you belong, which of the dark gods do you serve, and have you always been a part of that legion or chapter?)