[quote=@Prince of Seraphs]
[@Guess Who] What do you think the yellow eyed monster is? My guess is the consciousness of his adoptive father. A lot of David's rewritten memories center around him.
[/quote]

I've been hoping since the beginning that, whoever he is, he's some character that we've seen before in the comics. Considering that literally every other character in the cast was made specifically for the show I know that's unlikely now, but I still want to hope it's the Shadow King.