Hm. I'm not sure I see a really strong Godfather parallel. The personal ambitions there feel of a different type, although I might feel different if I watched that movie again and looked for the connections - it's been awhile since I've seen it.

And not really a horror archetype, no, although that's not really important - what does strike me is that the Godfather is actually a good symbol for God, period, or at least how a lot of god-based magic works, traditionally. You do Him a favor (sacrifice, prayer, etc.), He does you a favor....