The player character. First we free the knaifu for no reason and deliver her to N'zoth to awaken him and then, knowing that he's made the knife his tool, we bring it to Sylvanas anyway even as N'zoth tells us she's pure evil and how bad an idea it is.
https://www.wowhead.com/news=291224/...atath#comments
We do this regardless of whether we're #Shills4Syl or Rebelscum. Sylvanas doesn't even tell us to get the knife or anything. She would've lost the war due to her mental retardation if we didn't help her become an Old God puppet because the real twist is that we were the old god puppets all along.
And we did it all for 10g and 2000 azerite.