Persona. If you're familiar with Jungian philosophy it makes a bit more sense, since a Persona is a 'mask' you use to interact with the world. Demons, on the other hand, are spirits or fallen gods from mythology.

A Persona can take the form of a demon, but they're not the same. Persona are not physical entities that can act on their own, as they're linked to your soul - or mind, if you prefer to think of it that way.