Also called the dark lord, Tom Marvolo Riddle is the biggest fear of the entire series who first appeared in the 3rd part that is Harry Potter and the prisoner of Azkaban. He was the killer of Harry's parents and also wanted to kill Harry on the same day he killed his parents but unfortunately Harry was saved by his mother. So the Dark Lord always says that "The boy who lived comes to die".
He is so much powerful that no one can tale his name and in the entire series he is known as "You know Who" or "He Whose name can not be taken" or "The Dark Lord" because Voldemort or his followers may trace anyone who utters it. Lord Voldemort hated non-pure-blood wizards, despite being a half-blood himself and believes that the "Muggle" or the half blood should not be given the knowledge of witchcraft.He has created 7 Horcruxes of his soul which means that he can not be killed until all the 7 Horcruxes are vanished.Harry Potter is also one Horcruxes of lord Voldemort .Voldemort is an extremely powerful, intelligent, and ruthless Dark Wizard.he can read minds and shield his own from penetration. Besides Dumbledore he is also the only wizard ever known to be able to apparate silently. Voldemort was also said to fear one wizard alone, Albus Dumbledore.