[Looking into use of the word αυταρκεια this morning (cf. 1Ti 6.6) I came across Hermas Mandates 6.2 and had to post it. — RWB]

36. “Now hear,” he said, “about faith. There are two angels with man, one of righteousness and one of wickedness.” (2) “So how, sir,” I said, “will I recognize their workings, given that both angels live with me?” (3) “Listen,” he said, “and understand them. The angel of righteousness is sensitive and modest and gentle and tranquil. When this one enters your heart, immediately he talks with you about righteousness, about purity, about holiness, about contentment, about every righteous deed, and about every glorious virtue. Whenever all these things enter your heart, you know that the angel of righteousness is with you. These, then, are the works of the angel of righteousness. So trust him and his works. (4) Now observe the works of the angel of wickedness. First of all, he is ill-tempered and bitter and senseless, and his works are evil, tearing down God’s servants. So whenever this one enters your heart, recognize him by his works.” (5) “But I do not know, sir,” I said, “how to recognize him.” “Listen,” he said. “When some angry temperamental outburst or bitterness comes over you, recognize that he is in you. Then comes the desire for much business, and extravagant kinds of foods and drink, and much drunkenness, and various kinds of unnecessary luxuries, and the desire for women, and greed and arrogance and pretentiousness, and whatever else resembles or is similar to these things. So whenever these things enter your heart, you know that the angel of wickedness is with you. (6) Recognizing, therefore, his works, shun him and do not trust him at all, because his works are evil and harmful to God’s servants. You now have, then, the working of both angels; understand them and trust the angel of righteousness. (7) But shun the angel of wickedness, because his teaching is evil in every respect. For even if one is a man of faith and the thought of that angel enters one’s heart, it is inevitable that that man or woman will commit some sin. (8) On the other hand, if one is an extremely sinful man or woman, and the works of the angel of righteousness enter his heart, of necessity he must do something good. (9) You see, then,” he said, “that it is good to follow the angel of righteousness, but to shun the angel of wickedness. (10) This commandment explains the things about faith, in order that you may trust the works of the angel of righteousness, and that doing them, you may live to God. But believe that the works of the angel of wickedness are dangerous, so that by not doing them you will live to God.”

Holmes, M. W. (1999). The Apostolic Fathers : Greek texts and English translations (amazon.com) (Updated ed.) (391). Grand Rapids, Mich.: Baker Books.

So, the idea of the angel/devil on the shoulder — popularized for me by several Warner Bros. cartoons as I recall — goes back. Way back. Probably further back than Hermas (second century?).