This is a "Wild Mass Guess" entry, where we pull out all the sanity stops on theorizing. The regular entry on this topic is elsewhere. Please see this programme note.
Grand Unifying Guesses God aka: God
God is everywhere, so isn't it funny how you never see him in the same room as...
But that's impossible! Jesus wears glasses and God doesn't!
Plus Jesus is supposed to be God's son! How can he be God as well?!
Yog-Sothoth, who existed before time began and exists beyond all known creation. Created Azathoth, who created our own universe by accident, making him more of a God of god(s).
By extension, the Dunwich Horror is Jesus (this was probably intentional).
So Ryuk and Rem don't count? Besides, Light only has a God Complex; if he was really God, Ryuk or Rem would have noticed and said something. And God can't die