Odysseus swore an oath to protect Helen of Troy and her family at all costs. It made him leave Ithaca and go to the Trojan War.
Detailed answer:
Odysseus is an important character in Greek mythology. He appeared in two significant poems by Homer: The Iliad and The Odyssey. He received the throne of the kingdom of Ithaca from his father, Laertes. Odysseus showed courage and strength from a young age, so he was a good fit for Ithaca’s ruler. He even managed to save his family from an attack of a wild boar while hunting. Due to this, he has a permanent scar.
Once on the throne of Ithaca, Odysseus began to consider marriage. Following the example of other Greek heroes of the time, he desired Helen to be his wife. She was the daughter of Spartan King Tyndareus. However, being the ruler of a poor island, Odysseus had little to no chance of becoming Helen’s spouse. However, he decided to depart for Sparta.
Many suitors desired Helen, but Odysseus managed to show some wit. Later, he became famous as one of the greatest heroes of Greek mythology. King Tyndareus remained cautious about his daughter’s future. He feared something terrible might happen to Helen and her potential husband. To prove himself worthy, Odysseus suggested that every suitor take a sacred oath to protect Helen and the man who would marry her.
While visiting Sparta, Odysseus met Penelope, with whom the hero immediately fell in love. She was King Tyndareus’s niece. The King, who greatly appreciated his idea regarding the suitors’ oaths, made arrangements for their wedding. Shortly after, the couple returned home to the island of Ithaca. There, they had a son named Telemachus. All three would later become the main characters of Homer’s Odyssey.
At the same time, Helen married Menelaus. The rest of the suitors accepted him due to Odysseus’s idea regarding the oath. The daughter of King Tyndareus left Sparta with her new husband to become Helen of Troy. Sometime after, she ended up in the middle of the famous Trojan War.
Despite his oath, Odysseus had grown used to a happy life with Penelope and Telemachus. That is the reason he desired to avoid participation in the war. His resistance was caused by an Oracle’s prophecy, according to which Odysseus would spend twenty years wandering as a beggar afterward. When officials came to take him to war, Odysseus pretended he was a madman. Nevertheless, as the hero was working in the field, the officials placed his son Telemachus in front of the plow. Odysseus stopped and saved the boy, which was proof he had not gone mad.
Subsequently, Odysseus had to depart for the Trojan war, where the army recognized his wit and intelligence. His role was mostly an advisor who convinced Achilles to join the war, although he fought with courage. He was also the one to come up with the Trojan horse trick. When Troy fell, Odysseus attempted to return home, but his journey took a long time. The story of his voyage home became the plot of The Odyssey.