This paper explores the biography of Protagoras of Abdera as well as tragic irony as a poetic device in Plato's dialogues. I discuss ancient sources (Diogenes Laertius, Timo of Phlius, Plato) as well as modern interpretations related to the life - and especially the death - of Protagoras. Contrary to common consensus, I argue that the sophist's fleeing from Athens to escape conviction, and his accidental death at sea, are historical facts. Far from contradicting later accounts, Plato's references to Protagoras' long-lasting good reputation further support the evidence, e.g. when Protagoras, as a Platonic character, parades his unfailing success. Protagoras' ill-founded and slightly ridiculous over-confidence should be construed as an instance of irony on Plato's part: comparative material makes it clear that Plato is in fact maliciously hinting at the sophist's impending fate. In so doing, Plato proves to master the well-established technique of tragic irony, which he brilliantly adapts to the new genre of Socratic dialogue.