In Book 9 of Homer's Odyssey, Odysseus recounts his adventure to the land of the Cyclopes. While there, he and twelve of his men were imprisoned by Polyphemus the cyclops (who ate two of them and was saving the rest for later). Odysseus used his intelligence and cunning to blind the cyclops without arousing the suspicion of Polyphemus' neighbors; he told Polyphemus his name was "Nobody," which caused Polyphemus to yell: "Nobody is killing me!"
Odysseus later used his intelligence to scheme an escape from the cyclops' cave. Despite escaping without Polyphemus noticing, Odysseus wanted to brag about his intelligent plan; he wanted the cyclops to know whose cunning had bested him. Odysseus' men tried to prevent him from taunting Polyphemus, but he eventually gave into the temptation and told Polyphemus his real name:
Cyclops, if any mortal man ever asks you who it was that inflicted upon your eye this shameful binding, tell him that you were blinded by Odysseus, sacker of cities (Book 9, lines 503-504).
Unfortunately for Odysseus, Polyphemus had a powerful father: the sea-god Poseidon. Once Polyphemus told Poseidon how Odysseus had hurt him, the god promised to seek vengeance.