Same, I love that aspect of Fyodor's character a lot. There's a saying that the more brilliant mind the lonelier the soul and I think that encapsulates Fyodor's character quite well, especially if his immortality is taken into account. He's untouchable but that comes with the price - thirst inside him that would never be quenched.

As for Fyodor's goal, yes it is selfless at the face of it. However such strong motivation and diligence must come from deeply selfish reasons deep down. Ofc it's too early to tell and nothing can support my claims, but I believe just that loneliness (combined with maybe loss) have pushed Fyodor down that path, all under guise of abiding by God's will.