I have been wondering about it. They were the worshippers of the Void before Sargeras made thm to do his bidding. But did they truly agree to his plan or are spies of the Void?
It is really visible in them that they have never truly broke off with the spooky shadow, considering that most of their abilities are based on it. True, their eyes brim with fel, and they received immortality through it, but their arsenal is almost naked when it comes to fel powers, they prefer shadow.
I don't remember Chronicle well, what was their reason for joining BL?