Maou

This character is the king of demons.

Fiction about demons usually tells of a hierarchy in hell and a demon sits atop of all the others, this king is called Maou, basically the Japanese for demon king.

One thing to note is that Maou should not be mixed with Satan, because while Satan is a unique character from Christian Myth, the king of demons refers to a title held by, (usually) the most powerful demon in a wide range of myths.

This trait is intended to be used for a character who is the actual king of demons and not just a normal human who got it as a title, which seems to be a rather common title among dangerous elements.