Sameel

A Demon King of the abyss, is responsible for the start of the darksiders arc, where he summoned several demon Lords, hundreds if not thousands of high rank demons and countless mid and low rank demon's, having at least 3 fallen angel guards, With one being the fragment of an archangel.

It is suspected by Roy that Samael is the result of a Seven Deadly Sin Demon King splitting their soul into a few incarnations. He further suspected, after he split his soul into his clone that was made with the Red Sea Egg, that maybe the clones refused to fuse back into the Seven Deadly Sin Demon King in their pursuit of individuality. Maybe this is what caused the Seven Kings to disappear? They split into clones and the clones refused to fuse back.