A villein is a peasant bound to a feudal lord, owing labour or dues in return for the land he works — from Latin villanus, the worker on a villa, documented before 1325. Villain started as the very same word. The upper classes took “country dweller” to mean crude manners, then let crude manners stand in for bad character, and by the end of that journey the bumpkin had become Dr. No. A.Word.A.Day puts it in six words: the villein worked a plot, the villain plotted.