Stoic philosopher, and second head of the Stoic school. Coming between Zeno of Citium, the founder, and Chrysippus, the ‘second founder’ of the Stoic school, Cleanthes has usually been accorded a relatively minor position. However, his Hymn to Zeus contains an elaboration of Stoic physics, explaining the flux in terms of a principle of ‘tension’ (tonos) in the underlying substance of the world. He represents the pantheism of Stoicism, and the conception of ideal life as one lived in accordance with nature. He is himself recorded as a patient and gentle person, undeserving of his nickname ‘the ass’.