A diachronic approach to the relationship between literature and philosophy since antiquity needs to include the field of rhetoric, regardless of whether it appears as a link or a disruption. This article discusses fundamental questions of rhetoric, philosophy, and poetics in the example of invisible characters and their moral qualities in antiquity and the mid-18th century. Plato’s mythical literary version of the Gyges legend in the “Republic” conceives of the invisible character as an illustration of the morally depraved nature of humans. In the following, I shall not trace this “Gyges problem” in the terms of influence studies but rather with an awareness of the ubiquity of ancient knowledge in philosophy and literature of the 18th century. I shall situate Adam Smith’s oft-discussed metaphor of the invisible hand in the context of his lectures on rhetoric, which were instrumental in founding the tradition of the Scottish New Rhetoric. I shall argue that invisibility forms a central element of Smith’s definition of character. The manifold implications of such a conception of invisible characters will then be illustrated using the example of Eliza Haywood’s “The Invisible Spy” (1755) and her conception of authorial ethos. Thus, the metaphor of invisibility proves itself to be of transhistorical relevance for the relationship between philosophy and literature, especially when they both turn to character – understood as fictional person, moral constitution, and the medium of the letter.