Sybill Trelawney

Is Sybill Trelawney a true seer who possesses the inner eye, or a fraud like most people suggest? Albus Dumbledore would rather not have allowed the subject of Divination to continue at Hogwarts. He did give Sybill Trelawney the courtesy of an interview for a position to teach the class, as she is the great-great-granddaughter of Cassandra Trelawney, an acclaimed Seer. She, however, did not seem to inherit Cassandra's talent, so Dumbledore (kindly) rejected her for the position. As he was about to leave, though, she spoke in a harsh tone:

The one with the power to vanquish the Dark Lord approaches ... Born to those who have thrice defied him, born as the seventh month dies ... And the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not ... And either must die at the hand of the other for neither can live while the other survives ... The one with the power to vanquish the Dark Lord will be born as the seventh month dies...

Trelawney was overheard by, not only Dumbledore, but Severus Snape. For her own protection, Dumbledore allowed her to teach and live at Hogwarts. Snape, however, took what he had just heard to Lord Voldemort, causing Voldemort to attack Harry Potter and murder James and Lily (something for which Snape showed remorse later).

At Hogwarts, Sybill is often thought of as a fraud. She does have her followers who do believe in her, such as Lavender Brown and Parvati Patil. However, other people, like Minerva McGonagall often showed their dislike for the subject of Divination. And she was obviously aware of (and annoyed by) Trelawney's tendency to predict a student's death in the first class every year. In Harry's third year (his first year taking Divination), Hermione Granger often expressed her, um, negative feelings for Divination and Trelawney. Though, that's not to say Trelawney did not dish a little bit of it back to her. Harry, too, started to think that Trelawney did not possess the Inner Eye. However, he heard her speak in the same harsh voice that Dumbledore once heard:

it will happen tonight. the dark lord lies alone and friendless, abandoned by his followers. his servant has been chained these twelve years. tonight, before midnight... the servant will break free and set out to rejoin his master. the dark lord will rise again with his servants aid, greater and more terrible than ever he was. tonight... before midnight...the servant...will set out...to rejoin...his master....

Though Harry believed Trelawney was referring to Sirius Black at the time, she correctly predicted that Lord Voldemort's servant Peter Pettigrew would return to his master that night. Dumbledore pointed out that it seemed Trelawney had made her second real prediction, and joked about offering her a pay raise.

Few people expect much from Trelawney and Divination, she had no conflicts with other teachers and students quite like she had with Dolores Umbridge. As the new *ahem* Ministry-appointed teacher, and eventually High Inquistor and Headmistress, Umbridge obsessively exercised her authority by trying to get at least one of Hogwarts' teachers sacked. While reviewing Trelawney's performance, Umbridge insisted she make a prediction. Trelawney struggled with this, and gave a few of her usual predictions of death and misery. Umbridge finally got her way and sacked Trelawney, though not as smoothly as she would have hoped. Trelawney caused the dramatic scene in front of the whole school, while McGonagoll tried to comfort her. And with all the Ministry-appointed authority she had, Dumbledore did not allow Umbridge to kick Trelawney out of the castle. Trelawney remained at the castle, while Dumbledore quickly hired Firenze the Centaur to replace her as a teacher.
When Umbridge was finally removed from Hogwarts, Trelawney got her old job back and (to her displeasure) shared the Divination position with Firenze.

Whether she is a true Seer or not, Sybill Trelawney has her quirks, her followers, and her non-believers. She also seems to have a slight addiction to sherry, and was caught hiding her empty bottles in the Room of Requirement. She can also resourceful, using her crystal balls not only in class but also as weapons against Voldemort supporters and Death Eaters! And though she probably has no memory of making the prophecy at all, her prediction about "The one with the power to vanquish the Dark Lord" was a key component of the Harry Potter story.