Cassandra

Daughter of the Trojan king Priam and Queen Hecuba. Cassandra was very beautiful, but considered quite unbalanced. As a child, she was left over night in a temple of Apollo together with her brother Helenus. In the morning, their parents found the children entwined with snakes. The serpents were flicking their tongues into the children's ears, and so they were given the gift of prophecy.
When Paris returned to king Priam's court to regain his recognition as his son, it was Cassandra who declared him her brother. Even so, Priam had her locked in a chamber since she was quite mad.
Apollo fell in love with Cassandra when she was a grown woman, and once again spent a night in his temple. When she refused him, he cursed her, and from then on no one was to believe her prophecies. Also, anyone betrothed to her died, a fate Othryoneus, Coroebus and Eurypylus were to share.
Amongst the things she foresaw was the Trojan horse and Agamemnon'sdeath. After the fall of Troy, she was dragged out of the temple of Athena, where she had sought protection, and raped by Ajax the Lesser.
Agamemnon took her as a prisoner of war, and she bore him twin sons: Teledamus and Pelops. He then took her with him to Mycenae, and despite her warnings they were both murdered by Clytemnestra. Aegisthus killed the two babies.
When Heinrich Schlieman excavated Mycenae he was sure he found Cassandra's grave, since in it he found the skeleton of a woman and two infants.
From this mythological character we have the expression "Don't be such a Cassandra".