Helenus is a son of Priam and Hecuba. He appears as a brave fighter in the Iliad, but he is most known as a seer. He forewarned Paris not to go to Sparta, but he would not listen.
After the death of Helen, he vied to be her new husband. He lost to his brother Deiphobus, and in anger left Troy for Mt. Ida. Realizing that he could be a great asset, Odysseus captured him. When the Greeks asked him when Troy would fall, Helenus gave them a series of conditions, which must be satisfied before the Greeks could have their victory. Among the conditions were that Neoptolemus and Philoctetes must be persuaded to fight for the Greeks. All of these conditions were met, but still Troy did not fall. It took Odysseus' clever plan to finally crush the Trojans' defense.
After the war, Helenus was not made a slave, presumably for his help. In the Aeneid, Aeneas visits Helenus, now a king of his own land. Helenus tells Aeneas where to found a city, how to avoid Scylla, Charybdis and other perils.