Nicene and Post-Nicene Fathers, Vol. II:
City of God: Chapter 11

Chapter 11.—Of the Opinion of the Platonists, that the Souls of Men Become Demons When Disembodied.

He 350 says, indeed, that the souls of men are demons, and that men become Lares if they are good, Lemures or Larvæ if they are bad, and Manes if it is uncertain whether they de p. 172 serve well or ill.  Who does not see at a glance that this is a mere whirlpool sucking men to moral destruction?  For, however wicked men have been, if they suppose they shall become Larvæ or divine Manes, they will become the worse the more love they have for inflicting injury; for, as the Larvæ are hurtful demons made out of wicked men, these men must suppose that after death they will be invoked with sacrifices and divine honors that they may inflict injuries.  But this question we must not pursue.  He also states that the blessed are called in Greek εὐδαίμονες, because they are good souls, that is to say, good demons, confirming his opinion that the souls of men are demons.

Footnotes

Apuleius, not Plotinus.