Cleanthes of Assos (c. 330–230 BCE) was a Greek Stoic philosopher and the direct successor of Zeno of Citium as head of the Stoic school. Renowned for his moral rigor and remarkable endurance, he viewed philosophy as unwavering loyalty to reason and the cosmic order. His most famous work, the Hymn to Zeus, articulates a deeply religious vision of the Logos as the divine and rational principle governing the universe.