But when we say that there are demons— as though, in the simple fact that we alone expel them from the men's bodies, we did not also prove their existence— some disciple of Chrysippus begins to curl the lip. Yet your curses sufficiently attest that there are such beings, and that they are objects of your strong dislike. As what comes to you as a fit expression of your strong hatred of him, you call the man a dæmon who annoys you with his filthiness, or malice, or insolence, or any other vice which we ascribe to evil spirits. In expressing vexation, contempt, or abhorrence, you have Satan constantly upon your lips; the very same we hold to be the angel of evil, the source of error, the corrupter of the whole world, by whom in the beginning man was entrapped into breaking the commandment of God. And (the man) being given over to death on account of his sin, the entire human race, tainted in their descent from him, were made a channel for transmitting his condemnation. You see, then, your destroyer; and though he is fully known only to Christians, or to whatever sect confesses the Lord, yet, even you have some acquaintance with him while yet you abhor him!
Source: The Soul's Testimony (New Advent)