Mordekaiser title should be "Master of Puppets"
You know, all of his abilities are themed after heavy metal songs, so why not his title as well? Example: Mace of spades - Ace of spades by Motorhead Harvester of Sorrow - Harvester of Sorrow by Metallica Dragonforce - Power Metal band with the same name
So Just call him the Master of puppets (Master of Puppets by Metallica) which also fit with his theme of esnlaving souls