Why would Harry call Voldemort Riddle?

Question

“Severus Snape wasn’t yours,” said Harry. “Snape was Dumbledore’s, Dumbledore’s from the moment you started hunting down my mother. And you never realized it, because of the thing you can’t understand. You never saw Snape cast a Patronus, did you, Riddle?”

_{Deathly Hallows, chapter 36: "The Flaw in the Plan"}

Dumbledore used to call Voldemort Tom or Riddle because Voldemort was once Dumbledore's student whose name was Tom Riddle at the time. But, why would Harry call him Riddle?

Answer 1

Short version: psychological warfare.

Voldemort hates his muggle name, as Slytherincess points out in an answer to a related question:

'You think I was going to use my filthy Muggle father's name for ever? I, in whose veins runs the blood of Salazar Slytherin himself, through my mother's side? I, keep the name of a foul, common Muggle, who abandoned me even before I was born, just because he found out his wife was a witch? No, Harry. I fashioned myself a new name, a name I knew wizards everywhere would one day fear to speak, when I had become the greatest sorcerer in the world!'

^{_{Chamber of Secrets Chapter 17: "The Heir of Slytherin"}}

"Voldemort" is more than a name, it's an identity. It's a way of elevating himself above the people he hates, and past he hates more. "Voldemort" is powerful: the Dark Lord, the most feared wizard of all time, practically a god in the eyes of his followers, saviour of the Purebloods. "Tom Riddle" is powerless: a small, frightened, unloved, half-blood child.

Using that name effectively does two things:

1. It reminds Voldemort of how utterly powerless he is; no matter how hard he tries, he's still that frightened child
2. It rejects Voldemort's self-written mythology, and rejects his power to impose that mythology

Neither of those things are conducive to Voldemort's continued mental stability.

It's also probably because Dumbledore always did:

'It was foolish to come here tonight, Tom,' said Dumbledore calmly. 'The Aurors are on their way -'

'By which time I shall be gone, and you will be dead!' spat Voldemort.

[...]

'You do not seek to kill me, Dumbledore?' called Voldemort, his scarlet eyes narrowed over the top of the shield. 'Above such brutality, are you?'

'We both know that there are other ways of destroying a man, Tom,' Dumbledore said calmly

^{_{Order of the Phoenix Chapter 36: "The Only One He Ever Feared"}}

He does it again in Half-Blood Prince, even after Voldemort protests:

Dumbledore stood and swept over to the cabinet where he now kept the Pensieve, but which then was full of bottles. Having handed Voldemort a goblet of wine and poured one for himself, he returned to the seat behind his desk. "So, Tom... to what do I owe the pleasure?"

Voldemort did not answer at once, but merely sipped his wine. "They do not call me 'Tom' anymore," he said. "These days, I am known as —"

"I know what you are known as," said Dumbledore, smiling, pleasantly. "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."

^{_{Half-Blood Prince Chapter 20: "Lord Voldemort's Request"}}

This is just another type of psychological warfare. Dumbledore is often called "the only person Voldemort ever feared", so using Dumbledore's mannerism is another way of getting inside Voldemort's head.

Answer 2

I agree with all the psychological warfare points, and how that would be part of why he called him Riddle.

However, it is also true that Harry, probably more than any other than Dumbledore, knew Voldemort as Tom Riddle also, having viewed Tom from Dumbledore's perspective through his many private sessions with Dumbledore and his thoughts via the Pensieve.

Answer 3

He says to mock him. To show that he is not scared of him. To show that his current value is as good as Riddle and no longer as the mighty Voldemort.

Answer 4

I think the main point is covered in Jason's answer, Harry (like Dumbledore before him) wanted to remind Tom that he was just a person, and using his real name helped do that. Also Harry wanted to remind Voldemort (and everyone else) that Voldemort was a half-blood, and using his father's surname helped to accent that. But it is also the case that at Hogwarts surnames are used when someone is being told-off or bullied. "Come here Potter" sounds more aggressive than "Come here Harry". So I'd say there are three reasons:

1. To remind Tom that he's just the same as everyone else
2. To remind everyone (including Tom) that his father, Mr Riddle, was a muggle
3. To claim the school-master-like authority of using Riddle's surname to address him

Answer 5

I think Harry is also trying to remind and warn Voldemort that he is mortal like his father was before him. Despite Voldemort's desperate attempts to cheat death, Dumbledore and Harry have destroyed most of his horcruxes. Harry is giving him fair warning that the end is near.