Who do you think is the most powerful demon in existence? Also to note, when I mean powerful, I mean their raw strength, so having the Mark of Cain, injecting themselves with angel grace do not count as their raw strength. I personally think Samhain was the most powerful demon. Without any help from anything, he summoned zombies, ghosts and other creatures with just a though. He was also invulnerable to the demon-killing knife.