Odysseus was one of the original suitors of Helen of Troy. When Menelaus succeeded in winning Helen's hand in marriage, it was Odysseus who advised him to get the other suitors to swear to defend his marriage rights. However, when Menelaus called on the suitors to help him bring Helen back from Troy, Odysseus was reluctant to make good on his oath. He pretended to have gone mad, plowing his fields and sowing salt instead of grain. Palamedes placed Odysseus' infant son in front of the plow, and Odysseus revealed his sanity when he turned aside to avoid injuring the child.
However reluctant he may have been to join the expedition, Odysseus fought heroically in the Trojan War, refusing to leave the field when the Greek troops were being routed by the Trojans, and leading a daring nocturnal raid in company with Diomedes. He was also the originator of the Trojan horse, the strategem by which the Greeks were finally able to take the city of Troy itself. After the death of Achilles, he and Ajax competed for Achilles' magnificent armor; when Odysseus' eloquence caused the Greeks to award the prize to him, Ajax went mad and killed himself.
Odysseus' return from Troy, chronicled in the Odyssey, took ten years and was beset by perils and misfortune. He freed his men from the pleasure-giving drugs of the Lotus-Eaters, rescued them from the cannibalism of the Cyclopes and the enchantments of Circe. He braved the terrors of the underworld with them, and while in the land of the dead Hades allowed Thiresias, Odysseus' mother, Ajax and others to give him adivice on his next journey. They gave him important advice about the cattle of the sun (which Apollo herds), Scylla and Charybdis and the Sirens. From there on the travels were harder for Odysseus, but they would have been much worse of it wasn't for the help of the dead.
With this newly acquired knowledge, he steered them past the perils of the Sirens and of Scylla and Charybdis. He could not save them from their final folly, however, when they violated divine commandments by slaughtering and eating the cattle of the sun-god. As a result of this rash act, Odysseus' ship was destroyed by a thunderbolt, and only Odysseus himself survived. He came ashore on the island of the nymph Calypso, who made him her lover and refused to let him leave for seven years. When Zeus finally intervened, Odysseus sailed away on a small boat, only to be shipwrecked by another storm. He swam ashore on the island of the Phaeacians, where he was magnificently entertained and then, at long last, escorted home to Ithaca.
There were problems in Ithaca as well, however. During Odysseus' twenty-year absence, his wife, Penelope, had remained faithful to him, but she was under enormous pressure to remarry. A whole host of suitors were occupying her palace, drinking and eating and behaving insolently to Penelope and her son, Telemachus. Odysseus arrived at the palace, disguised as a ragged beggar, and observed their behavior and his wife's fidelity. With the help of Telemachus and Laertes, he slaughtered the suitors and cleansed the palace. He then had to fight one final battle, against the outraged relatives of the men he had slain; Athena intervened to settle this battle, however, and peace was restored.