Dionysius the Renegade
Dionysius the Renegade (Dionysius of Heraclea, c. 330 – c. 250 BC; Greek Metathemenos, “the Turncoat”) was an early Stoic philosopher, a pupil of Zeno of Citium (Stoicism’s founder). Late in life, afflicted by terrible eye pain, he abandoned Stoicism — whose ethics hold that virtue alone is good and pain is not truly an evil — and joined the Cyrenaics, who held that pleasure and the absence of pain are the highest good. The defection earned him his nickname. Praised for modesty and moderation while a Stoic, he was later called a man given to pleasure; he reportedly died at eighty by voluntary starvation.
Why he’s interesting
He’s the school’s own apostate — a living stress-test of the Stoic claim that a sage remains unmoved by pain. That doctrine failed him under real suffering, which is exactly why later writers kept his story: the counter-example that sharpens what Stoicism was asking of people. Source: Wikipedia (T2, tertiary, drawing on Diogenes Laërtius; a minor figure — thin record).