This most prominent of the Stoic philosophers studied in Athens with Kleanthis, and perhaps with Zeno as well, and wrote 500 lines per day, resulting in a total production of some 705 works, about half of which were dialectical writings, though only a few fragments have been saved.
He style was rather dry and ungraceful. He was the thinker who formulated Stoic doctrines, and who guided the school towards a scientific orientation. He believed that nothing was by chance, and that if the cause of something was not apparent, it still existed, that diseases served some divine agenda, either as punishment or as an opportunity to act morally. The universe was seen as one, ruled by divine Reason.