Cleanthes was a pugilist (athletic philosophers must have been a thing, Plato was a wrestler!), and arrived in Athens quite poor. As a result, he worked at night, drawing water in the gardens, in order to be able to afford philosophy during the day.
Cleanthes was made fun of by his fellow pupils because his low station in life, but apparently did not mind. He was critical of others, but also had a good sense of humor and self-deprecation. As Diogenes says: “He would often find fault with himself too, and one day when Ariston heard him doing this and asked, ‘Who is it you are scolding so?’ he, laughing, said, ‘An old man with grey hairs and no wits.'”
One anecdote puts him in the theater when Sositheus publicly made fun of him on stage. Cleanthes was so, well, stoic about it, that the astonished audience actually drove the offending artist off stage.
When asked, as an old man, whether he was ready to die, he replied: “I too am ready to depart; but when again I consider that I am in all points in good health and that I can still write and read, I am content to wait.” Like Zeno (allegedly), Cleanthes died of old age by starving himself.