Chrysippus of Soli (lived 280-206 B.C.E.) headed the stoic school after Cleanthes, from 232 B.C.E. until his death. He wrote about 705 books more than any other philosopher, none of which survive. Diogenes Laertius (a Greek biographer) cited Carneades as saying that Chrysippus merely repeated himself a lot and copied what others had said in order to write more works than Epicurus, who had written more books than anyone ever had written before. He was a pupil of Arcesilaus before he became a Stoic philosopher under Cleanthes. He did great work in logic and made it central in study. He believed that the emotions play a role in indicating things' value, and he put emphasis on empirical knowledge. He believed that Zeus was the Supreme Fire and was the only immortal god. And that Zeus had nothing to do with the causation of evil, but that evil is necessary because good can't exist without evil.