Tiresias is a blind prophet of Apollo who lived in Thebes. He appears in many Greek myths and is famous for his clairvoyance. He is dead by the time the events of The Odyssey take place, and is an inhabitant of the underworld. Odysseus travels there specifically to meet with Tiresias in Book 11 after Circe tells him that only Tiresias can explain how Odysseus might get back to Ithaca.
Tiresias’s presence in The Odyssey is brief but essential. He is a powerful seer, and he uses his gifts to give Odysseus crucial advice. First and foremost, he tells him why Poseidon is targeting him—because Odysseus blinded the Cyclops, Polyphemus—and how to get past Scylla and Charybdis, two monsters known for destroying ships. He also makes a prediction: that Odysseus will make it back to Ithaca and get revenge on the suitors who are trashing his feast room and courting his wife. Tiresias’s predictions effectively outline the plot for the rest of the narrative.
Odysseus’s episode with Tiresias is further significant because it includes a key piece of foreshadowing. Tiresias explains that Odysseus and his crew are destined to land on the island of Thrinacia. He warns Odysseus not to slaughter any of the cattle they find there because they are sacred and belong to the sun god. Ultimately, in Book 12, Odysseus’s men eat the cattle against his orders, causing Zeus to destroy Odysseus’s ship and crew. Tiresias’s warning underscores concepts like fate and prophecy, as well as justice. Just as Odysseus’s men take what isn’t theirs, so too do the suitors, and they all pay the price for it. Similarly, Odysseus will answer for his transgression—to appease Poseidon, Tiresias says that, once home, Odysseus must make another trip to a distant land, must travel until he finds a place where none have heard the of sea and do not recognize his oar, and make a sacrifice to Poseidon.