The Shadow is the Hero of Amnesia {Lore/Theory - Spoilers All}

IMPORTANT NOTE: This theory is not entirely my own, I owe it to the Amnesia wiki and one guy in a youtube comments section I can't find anymore for putting much of this information together. Still, I've added my own speculation, and felt that in general there should be an easily accessible place to hear about this theory.
My Twitter, if you care:   / kythytil  

Music Used:
All My Tears by Mikko Tarmia (Penumbra: Overture OST)
Menu Theme by Mikko Tarmia (Amnesia: the Dark Descent)
Herbert’s Headquarters by Mikko Tarmia (Amnesia: Rebirth)
Safe Room by Mikko Tarmia (Amnesia: The Bunker)
Ever Mine by Jessica Curry (Amnesia: A Machine for Pigs)
Empty Cots by Jessica Curry (Amnesia: A Machine for Pigs)
Back Hall by Mikko Tarmia (Amnesia: The Dark Descent)

Images/Videos Used:
Daniel’s Note to Self
https://amnesia.fandom.com/wiki/Danie...
Brennenburg Loading Screen
https://amnesia.fandom.com/wiki/Loadi...
Herbert in Rebirth
https://amnesia.fandom.com/wiki/Thurs...
Alchemist’s Memory Capsules
   • Amnesia Rebirth Walkthrough Gameplay ...  
Laudanum
https://amnesia.fandom.com/wiki/Laudanum
Shadow
https://amnesia.fandom.com/wiki/The_S...
Daniel
https://amnesia.fandom.com/wiki/Danie...
Other gameplay was recorded myself, particularly the still shots and Bunker end sequence.