Hes not just any clone. During the Clone Wars they were given the up most respect and that Captain is what you will give him.

RC/07 Sev. You served the Republic once. You can do so again for the Empire. I'm giving you an opportunity...not a choice. You can put your blaster down now..or you can rot in this forsaken wasteland. Its your decision.

You were part of a Clone group named Delta Squad the best that the Republic could offer. During Operation: Knightfall the Deltas inhibitor chips malfunctioned and saved a Jedi. They are a threat to the empire and must be terminated. And to prove your loyalty to the Empire you will kill the Jedi and your brothers. If you do not accept my offer..your already dead.