About
Lord Voldemort: "They do not call me 'Tom' any more," he said. "These days, I am known as -"
Albus Dumbledore: "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."
Tom Riddle met Albus Dumbledore at the age of eleven, when the Professor came to invite him to attend Hogwarts School of Witchcraft and Wizardry. Although initially suspicious of Dumbledore, he was at least somewhat impressed by Dumbledore's demonstration of magic. Tom was pleased to discover that he was a wizard, as it confirmed the suspicions he had long had about being "special." The boy disturbed Dumbledore, however, when he admitted to being able to hurt people who angered him and to talk to snakes. Even as Tom became an extremely popular student among his peers and Professors at Hogwarts, Dumbledore remained wary of him, and kept a very close watch on him.
Albus Dumbledore: "Rumours of your doings have reached your old school, Tom. I should be sorry to believe half of them."
Lord Voldemort: "Greatness inspires envy, envy engenders spite, spite spawns lies. You must know this, Dumbledore."
Riddle (then known as Voldemort) returned to Hogwarts years after graduating to request the Defence Against the Dark Arts position from Dumbledore, who had become the school's Headmaster. Suspecting that Voldemort's true intentions were far more sinister than he let on, Dumbledore refused him the position; the result of Dumbledore's refusal was not only that the position of DADA professor became "cursed," but it affirmed Dumbledore's complete refusal to bend to Voldemort's will.
Lord Voldemort: "But nothing I have seen in the world has supported your famous pronouncements that love is more powerful than my kind of magic, Dumbledore."
Dumbledore: "Perhaps you have been looking in the wrong places...,"
Lord Voldemort: "Well, then, what better place to start my fresh researches than here, at Hogwarts? Will you let me return? Will you let me share my knowledge with your students?"
Voldemort despised Dumbledore, not only for latter's continued opposition, but also because Dumbledore's belief in the triumphant power of love was something that both confused and disgusted Voldemort. Dumbledore was thought to be the only person Voldemort ever feared and one of the few people Voldemort was unable to intimidate. Dumbledore persisted on referring to him as "Voldemort" to others and addressing him as "Tom" in conversation, a subtle but steadfast refusal to allow Voldemort to dictate the terms of their relationship, and a trait that would later be inherited by Harry Potter. Dumbledore led the efforts against Voldemort in the First Wizarding War; over many years, Dumbledore gathered crucial information about Voldemort's past and passed it on to Harry Potter, who would essentially take Dumbledore's place as leader of the opposition in the Second Wizarding War.
Albus Dumbledore: "It was foolish of you to come here tonight, Tom. The Aurors are on their way."
Lord Voldemort: "By which time I shall be gone, and you shall be dead."
In 1996, Dumbledore and Voldemort met face to face in the Ministry of Magic during the Battle of the Department of Mysteries, where Dumbledore addressed Voldemort as "Tom" and said it was foolish of him to come to the Ministry. Voldemort initiated a duel with Dumbledore, during which he tried to murder both Dumbledore and Harry, but was unsuccessful; Dumbledore's power equalled, his own, and Harry was able to exorcise the Dark Lord from his body and mind by focusing on his intense feelings of grief over Sirius' death. Cornelius Fudge arrived at the Ministry in time to see Voldemort escape with Bellatrix Lestrange, and was finally forced to acknowledge the truth of Voldemort's return.
Lord Voldemort: "You do not seek to kill me, Dumbledore? Above such brutality, are you?"
Dumbledore: "We both know there are other ways of destroying a man, Tom. Merely taking your life would not satisfy me, I admit."
Lord Voldemort: "There is nothing worse than death, Dumbledore!"
Dumbledore: "You are quite wrong. Indeed, your failure to understand that there are things much worse than death has always been your greatest weakness."
Following his failure to kill either Dumbledore or Harry at the ministry, Voldemort assigned Draco Malfoy to carry out Dumbledore's assassination. Dumbledore became aware of this plot, and addressed it by arranging his own death with Severus Snape. At the time of his death in 1997, Albus Dumbledore had fully equipped Harry Potter with the physical, emotional and mental tools he needed to defeat Voldemort once and for all in 1998.
Source: Wikia.