This stonesinger, a powerful dredge spellweaver, is proof that not all the dredge fear and hate humanity. Though the stonesinger does not speak it travels with the Ravens now, working toward what you expect is the same goal: saving its own kind from the darkness.
[SPOILERS]
Apostate is first encountered by the Ravens in The Banner Saga 2 deep within the mines of Bindal. If allowed into the caravan via Zefr's translations, he joins the hero roster in The Banner Saga 3 alongside Iver and the Ravens.
He can be killed when introduced instead of being allowed into the caravan or during Chapter 13 if he is allowed to help fight the pursuing dredge and the battle is lost, he will get labeled as a traitor by them and killed.