How can Ron know that Voldemort was in Slytherin if nobody knows his real identity?

Question

When Ron meets Harry on the Hogwarts Express in Harry Potter and the Philosopher's Stone, they have this conversation:

“What House are your brothers in?” asked Harry.

“Gryffindor,” said Ron. Gloom seemed to be settling on him again. “Mum and Dad were in it, too. I don’t know what they’ll say if I’m not. I don’t suppose Ravenclaw would be too bad, but imagine if they put me in Slytherin.”

“That’s the House Vol-, I mean, You-Know-Who was in?”

“Yeah,” said Ron. He flopped back into his seat, looking depressed.
_{- Harry Potter and the Philosopher’s Stone, Chapter 6 (The Journey from Platform Nine and Three-Quarters)}

So Ron apparently knows Voldemort was in Slytherin. But at the end of Harry Potter and the Chamber of Secrets, it is made clear that Voldemort's real identity as the brilliant (Slytherin) student Tom Riddle is unknown to most - in Dumbledore's own words:

‘Very few people know that Lord Voldemort was once called Tom Riddle. I taught him myself, fifty years ago, at Hogwarts. He disappeared after leaving the school … travelled far and wide … sank so deeply into the Dark Arts, consorted with the very worst of our kind, underwent so many dangerous, magical transformations, that when he resurfaced as Lord Voldemort, he was barely recognisable. Hardly anyone connected Lord Voldemort with the clever, handsome boy who was once Head Boy here.’
_{- Harry Potter and the Chamber of Secrets, Chapter 18 (Dobby’s Reward)}

So how could Ron (as well as, I guess, most wizards) not know Voldemort's real identity yet know the actual House he was in at Hogwarts?

Answer 1

The Dark Lord himself might have said he was in Slytherin.

When the Dark Lord was at the height of his power, though he might not have wanted to talk much about his father or Muggle heritage, he was proud to be the descendant of Salazar Slytherin. He had been even as Tom Riddle, and though he wanted to be rid of his father’s name, he was quite proud of his relation to Slytherin. He called himself "Lord Voldemort, heir of Salazar Slytherin", indicating that he intended to keep the Slytherin connection even after he became Lord Voldemort.

“Now, Harry, I’m going to teach you a little lesson. Let’s match the powers of Lord Voldemort, heir of Salazar Slytherin, against famous Harry Potter, and the best weapons Dumbledore can give him.”
_{^{- Harry Potter and the Chamber of Secrets, Chapter 17 (The Heir of Slytherin)}}

He carried this pride into adulthood as well. When he takes over Hogwarts many years later, he announced that there will be no more houses, only Slytherin.

“There will be no more Sorting at Hogwarts School,’ said Voldemort. ‘There will be no more houses. The emblem, shield and colours of my noble ancestor, Salazar Slytherin, will suffice for everyone, won’t they, Neville Longbottom?”
_{^{- Harry Potter and the Deathly Hallows, Chapter 36 (The Flaw in the Plan)}}

It didn’t seem like the Dark Lord was trying to keep his Hogwarts house secret. Even if he didn’t want the wizarding world knowing that he was once Tom Riddle, he was likely perfectly happy to say he was a Slytherin.

Him saying it himself would explain why people seem so certain about his house, rather than it being treated like a widely believed rumor (like the circumstances of his disappearance, or Harry being thought to be the heir of Slytherin by his classmates). His claim to be the heir of Slytherin and ability to speak Parseltongue would help support the idea he was in Slytherin to anyone who knew of them, but the simplest way that people could seem to know his house is for him to have said it.

Answer 2

I don't think we can exclude the possibility that Ron - and more-or-less everyone, actually - simply assumed that he was in Slytherin. It obviously has a reputation for generating villains. Recall this statement:

"‘Better Hufflepuff than Slytherin,’ said Hagrid darkly. ‘There’s not a single witch or wizard who went bad who wasn’t in Slytherin. You-Know-Who was one.’"

_{—Harry Potter and the Philosopher's Stone}

Answer 3

Voldemort was indeed a known Parselmouth

Tom Riddle was a half-blood. The Riddle name did not belong to a known pureblood family. Therefore, Voldemort needed to show that he was great in some way, in order to convince witches and wizards to follow him.

After graduating from Hogwarts and disassociating himself from the Riddle name, he could have publicly flaunted his ability to speak in Parseltongue. This would serve as proof that Voldemort was descended from Salazar Slytherin himself, and provide credibility to his image as the champion of pure-bloods, as Salazar Slytherin was also popularly believed to have hated muggleborns due to the legend of Slytherin's monster being created to purge muggleborns from Hogwarts.

“It matters,” said Hermione, speaking at last in a hushed voice, “because being able to talk to snakes was what Salazar Slytherin was famous for. That’s why the symbol of Slytherin House is a serpent.”

_{-Hermione Granger, Harry Potter and the Chamber of Secrets}

Therefore, Ron and the entire wizarding world must have taken Voldemort's status as a Parselmouth as proof that he was descended from Salazar Slytherin.

---

Parseltongue, the ability to converse with snakes, has long been considered a Dark Art. Indeed, the most famous Parselmouth of our times is none other than You-Know-Who himself.

-_{The Daily Prophet}

_{Harry Potter and the Goblet of Fire, Page 612}

This particular quote proves that Voldemort was a known Parselmouth.

Answer 4

The Dark Mark

When Voldemort was in power, there were attacks everywhere, and when Death Eaters attack somewhere they cast the Dark Mark, which is Voldemort’s symbol with a snake on it. I think people could make deductions about his house afterwards.

There is citation somewhere in the books about the Dark Mark being seen very frequently at Voldemort’s golden years. If someone finds and edits this answer , It will be a more complete answer.

Answer 5

Dumbledore may have been correct that few people knew Voldemort's identity during his reign of Terror and even afterward. However, the British wizarding community is too small for it to have been kept a secret in retrospect. With only a few thousand individuals, it would be relatively straightforward to track down everyone who were still living or confirmed dead after the dark lord's defeat. Voldemort would have to be among those unaccounted for.

Most wizards seemed to want to know as little as possible about Voldemort after his passing. However, a curious individual like Arthur Weasley (who also had access to Ministry of Magic population records) ought to have been able to work it out. He presumably shared the information about what house Voldemort had been in with his family, but out of some misplaced sense of propriety did not reveal Voldemort's original name.

Answer 6

Arthur and Molly Weasley were in the original Order of the Phoenix. Assuming Dumbledore told the Order that Voldemort was previously known as Tom Riddle (in a know-your-enemy discussion), then it is reasonable to assume that all the Weasley children knew as well, especially after a dozen years of Voldemort's absence.

Answer 7

Possibly Voldemort issued a proclamation that mentioned that he was the natural leader of all (or all British?) wizards and gave some justifications for that, possibly including a claim that he had once been the top student in Slytherin, the house that the greatest wizards all came from and the house whose members were the rightful leaders of the wizards.

Thus everyone would know that Voldemort was a former Slytherin student who would have graduated sometime in the previous century or so (since it might be somewhat rare for wizards to live more than about a century after graduating about age 18), without knowing which former Slytherin student it was.

Answer 8

Inferred, from Death Eaters' ties to Slytherin House

The majority of confirmed⁽¹⁾ and suspected⁽²⁾ Death Eaters seem to have been former students of Slytherin House, and some came from the most proudly aristocratic levels of magical British society. These people saw their privileges as rightful, they were determined to increase their power, and they spent their Hogwarts years networking with other Slytherins of similar mind⁽³⁾. Whether or not such a collection of ambitious traditionalist bigots was capable of rallying for years around a non-Slytherin leader, the general magical public would have inferred that the Death Eaters could only follow a leader who came from Slytherin.

---

⁽¹⁾ IE, those who were convicted (such as the escapees from Azkaban in the 1997 mass breakout) or pardoned (Snape).

⁽²⁾ EG, Lucius Malfoy.

⁽³⁾ EG, Tom Riddle's core group.

Answer 9

There's always the "Lee Jordan argument": if all signs point to Slytherin then it's Slytherin. As formulated in Chapter Fourteen of Chamber of Secrets:

"That's two Gryffindors down, not counting a Gryffindor ghost, one Ravenclaw, and one Hufflepuff," said the Weasley twins' friend Lee Jordan, counting on his fingers. "Haven't any of the teachers noticed that the Slytherins are all safe? Isn't it obvious all this stuff's coming from Slytherin? The Heir of Slytherin, the monster of Slytherin – why don't they just chuck all the Slytherins out?" he roared, to nods and scattered applause.

Similarly, when it comes to Voldemort's house the signs point to Slytherin:

• Virtually all the Death Eaters were from Slytherin.

• Slytherin was known as the house that produced Dark wizards.

• Voldemort and the Death Eaters aligned with Slytherin views about blood purity and Muggle inferiority.

• The Dark Mark's symbol was a serpent, just like Slytherin's symbol.

Of course, it's also possible that someone who knew spread the word.