Cassandra is mentioned briefly in the Iliad of Homer (which, incidentally, is one of our oldest and most respected sources for information about the characters of Greek myth). Indeed, in the Iliad, we learn that Cassandra was the child of King Priam of Troy, and she was considered to be Priam's most beautiful daughter. However, no mention of Cassandra's notorious prophetic power is made in this Homeric epic.

We first find the tale of Cassandra and her legendary gifts in other works of ancient Greek literature. According to one version of the story, Cassandra received the power to foretell the future from the god Apollo. Apparently, Apollo instructed the mortal woman and taught her about the art of prophecy because he had an ulterior motive - the god wished to win her affections. Cassandra accepted Apollo as a teacher, but not as a lover. Naturally, the god was insulted by this refusal. So he punished Cassandra. Apollo caused the gift that he gave Cassandra to be twisted, making everyone who heard her true and accurate foretellings of future events believe that they were instead hearing lies. In other words, the wondrous blessing bestowed upon a mortal became instead a terrible curse.