Source: All of canon, really.
Disclaimer: Tolkien doomed Man and blamed Eru.
Author's Note: For the 'doom' challenge, fairly obviously.
Many names I am given, and most are spoken in anger or despair; for mortal men rail against the path they walk. Do they not know their end was a gift from their Lord? That it is blessing which I bestow? Would they have the Elven life, to walk forever and witness all they love whither and die? Better to remember sweeter times and take with grace the gifts I grant them.
Many names I am given: Fate and Wyrd and Destiny; but only one do I require; for I am Doom, and all must face me ere their end.