Who He Is
Tiresias is the blind prophet of Thebes, the only dead man in Hades who keeps his mind, a gift of Persephone, while the other souls flit about like shadows. Odysseus goes to him on the orders of Circe, who says the prophet will tell him the way and the return. He appears holding a golden staff and drinks the blood from the trench in order to speak. What he says organizes the rest of the poem: the wrath of a god, the cattle of the Sun, the house taken over, the vengeance, and one last journey.
Trajectory
In Book X, Tiresias does not yet appear, but he is the object of Circe's request: before setting out, Odysseus must go to the house of Hades to consult the soul of the Theban prophet, to whom Persephone gave the power to keep his mind after death. Odysseus falls weeping on the bed, and Circe gives him the route to the trench, the libations, and the black rams.
In Book XI, the soul of Tiresias arrives after Elpenor, recognizes Odysseus, asks why he came, leaving the light of the sun, and orders him to pull his sword away from the trench so he can drink the blood. He prophesies that Odysseus seeks a sweet return, but a god will make it harsh, because Poseidon holds a grudge against him for blinding his son. Still, they will arrive, if they hold back their spirit on the island of Thrinacia and leave the cattle of the Sun unharmed. If they harm them, he foretells the ruin of the ship and the companions, and Odysseus will return late and badly, with no one, on another man's ship, and will find troubles at home.
εἰ δέ κε σίνηαι, τότε τοι τεκμαίρομʼ ὄλεθρον, / νηί τε καὶ ἑτάροις. αὐτὸς δʼ εἴ πέρ κεν ἀλύξῃς, / ὀψὲ κακῶς νεῖαι, ὀλέσας ἄπο πάντας ἑταίρους, / νηὸς ἐπʼ ἀλλοτρίης· δήεις δʼ ἐν πήματα οἴκῳ,(11.112-115), but if you harm them, then I foretell your ruin, for the ship and the companions. And you yourself, even if you escape, will return late and badly, having lost all your companions, on another man's ship; and you will find troubles in your house,
After the vengeance on the suitors, Odysseus must carry a well-made oar until he comes to men who do not know the sea and do not eat food mixed with salt, and when a traveler calls the oar a winnowing shovel, he must plant it in the earth and sacrifice to Poseidon a ram, a bull, and a boar. Death will come to him from the sea, very gentle, when he is worn out by a shining old age, with happy peoples all around.
ἔρχεσθαι δὴ ἔπειτα λαβὼν ἐυῆρες ἐρετμόν, / εἰς ὅ κε τοὺς ἀφίκηαι οἳ οὐκ ἴσασι θάλασσαν / ἀνέρες, οὐδέ θʼ ἅλεσσι μεμιγμένον εἶδαρ ἔδουσιν·(11.121-123), then go, taking a well-made oar, until you come to men who do not know the sea, nor eat food mixed with salt.
θάνατος δέ τοι ἐξ ἁλὸς αὐτῷ / ἀβληχρὸς μάλα τοῖος ἐλεύσεται, ὅς κέ σε πέφνῃ / γήραι ὕπο λιπαρῷ ἀρημένον· ἀμφὶ δὲ λαοὶ / ὄλβιοι ἔσσονται.(11.134-137), death itself will come to you from the sea, very gentle, the kind that will kill you worn out by a shining old age; and around you the peoples will be happy.
In Book XII, on seeing the island of the Sun, Odysseus reminds the men what the blind Tiresias and Circe said, and that the worst of evils awaits them there. The prophecy comes true shortly after: the companions kill the cattle, and the ship is destroyed by a thunderbolt of Zeus.
In Book XXIII, after the recognition, Odysseus tells Penelope that one trial still remains, the one Tiresias prophesied to him on the day he went down to Hades, and he repeats the journey of the oar and the sacrifice. Penelope answers that if the gods make old age better, there is hope of escaping evils.
ὦ γύναι, οὐ γάρ πω πάντων ἐπὶ πείρατʼ ἀέθλων / ἤλθομεν, ἀλλʼ ἔτʼ ὄπισθεν ἀμέτρητος πόνος ἔσται, / πολλὸς καὶ χαλεπός, τὸν ἐμὲ χρὴ πάντα τελέσσαι.(23.248-250), woman, we have not yet reached the end of all the trials: there will be a labor without measure still to come, much and hard, which I must complete in full.
Themes Embodied
Tiresias embodies Vengeance, which he announces as certain, and shows what the poem calls a double determination: his prophecy makes the return depend on an abstention, leaving the cattle unharmed, and puts the responsibility on the leader, who must restrain his own spirit and that of his companions. He embodies the Home, exile and return, by saying that the house is taken over and that, after the vengeance, there will still be another journey.
Tiresias's prophecy opens two possibilities and foresees destruction only in the second, and the description of the end of the journey, late, without companions, on another man's ship, with the house taken over, repeats the curse of Polyphemus, now spoken by a prophet. The phrase that closes the prophecy, the death ex halós, admits two readings, coming from the sea or far from the sea, and the text does not decide. Either way, after so much suffering, the promised death is gentle, in old age.