Welcome Nikkolas!
I never really thought about it before, but I think that there isn't really a single main antagonist, just various manifestations of the primary antagonist that is Death. This includes Charlie's own grief, guilt, and confusion, the Morrigans, and the bull-headed death, plus, I'm sure, many others.
If you use a screen reader, see if you can set it on "cool Brit" for my posts. 
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Twitter: jefftunes