Cassandra

In Greek mythology, a daughter of Priam, king of Troy. She received the gift of foreknowledge from Apollo, the god of prophecy. There are two accounts of the way in which this happened. According to one, when she was a child, a birthday feast was held for her and her brother Helenus in a sanctuary of the god. The children fell asleep in a corner, and the sacred serpents licked their ears, giving them both prophetic powers.
The other version says that Cassandra’s sleep in the sanctuary occurred after she was grown up. Apollo desired her and promised her the prophetic gift if she would comply. She accepted it but then had second thoughts about her own side of the bargain. Apollo spat in her open mouth, with the result (implied also in the alternative story) that while she could foretell the future, no one would believe her.
Cassandra uttered her pronouncements in fits of frenzy suggesting insanity. Their ominous tone made her proverbial as a voice of doom. When the Greeks besieged Troy to recover the abducted Helen, Cassandra predicted the city’s fall, correctly but without effect.

Shakespeare introduces her briefly in Troilus and Cressida. While King Priam and his sons are discussing whether to continue the war or restore Helen to her husband and end it, Cassandra enters “raving, with her hair about her ears” and prophesies disaster unless Helen is returned. Her most important brother Hector is willing to listen, but another brother, Troilus, dismisses her “brain-sick raptures,” and the war goes on.
The Trojans had a last chance when they maneuvered the wooden horse through their gateway, unaware that Greek warriors were hidden inside it. Cassandra warned of what would happen if it were brought into the city, and was ignored as usual. During the night, the Greeks emerged from it and opened the gates to let their comrades in. Troy fell. The Greek commander-in-chief, Agamemnon, seized Cassandra as a prize of war and took her home with him. They were both killed by Agamemnon’s estranged wife and the lover she had taken during his absence. According to the dramatist Aeschylus, Cassandra foresaw her own fate.