"I know what you are known as. But to me, I'm afraid, you will always be Tom Riddle. It is one of the irritating things about old teachers. I am afraid that they never quite forget their charges' youthful beginnings."
-- Albus Dumbledore (HBP20)
Lord Voldemort sets up a meeting with the recently-appointed Headmaster, Albus Dumbledore, to ask for the Defense Against the Darks Arts position at Hogwarts. However, Dumbledore pointed out that Voldemort was certainly aware that the headmaster would never have offered that position to him and asked what his true purpose was for visiting. Voldemort did not say what it was, but later events reveal that Voldemort visited the Room of Requirement and hid the diadem Horcrux there. As he left, Voldemort put a curse on the Defense Against the Dark Arts position such that for the next twenty-five years, no teacher stayed in the post for more than one year.