Quintus Lucilius Balbus stands within the depth-psychology corpus primarily as the Stoic interlocutor in Cicero’s De Natura Deorum, where he functions as the authoritative mouthpiece for Stoic theology and natural philosophy. As a literary-philosophical figure, Balbus does not belong to the clinical register of depth psychology proper, yet the corpus engages him because his arguments concerning divine rationality, cosmic providence, and the innate human conception of the gods traverse questions of psychic universality, the archetype of the self, and the relationship between reason and religious instinct that depth-psychological thinkers inherit. In the dialogue, Balbus systematically deploys Cleanthes’ four sources of theological conception, the teleological argument from natural order, and Chrysippean analogies from biological development to defend Stoic pantheism against Academic scepticism and Epicurean atomism. The critical edge in these exchanges — supplied chiefly by Cotta — anticipates later psychological critiques of projected divinity. Long and Sedley’s reconstruction of Stoic physics in The Hellenistic Philosophers renders Balbus’s positions as philosophically precise rather than merely rhetorical, grounding them in the Stoic doctrine of the commanding-faculty, pneuma, and cosmic sympathy. The figure of Balbus thus marks a crucial ancient node connecting cosmological rationalism to the psychology of religious experience.