It wasn't like anyone really wanted to know anyway - until Harry and Ron did, of course. Like most people, Hagrid didn't know that Tom Riddle was Voldemort. Therefore, he really didn't need to know or care that much about Riddle besides what happened to get Hagrid expelled.
In fact, at the beginning of the series, barely anyone but Dumbledore and Hagrid knew that Voldemort was the charming, successful Tom Marvolo Riddle.
"Hagrid is one of Voldemort's oldest associates, and knows his true identity" In Chamber of Secrets, it is revealed that Hagrid had been a student at Hogwarts during the same period that Tom Riddle (the true identity of Lord Voldemort) also frequented the school.
But following the explanation about what happened in the Chamber of Secrets and the revelation that Voldemort himself was Slytherin's heir controlling the monster it would be clear. Hagrid would then know that Voldemort/ Tom Riddle had opened the chamber 60 years ago, and had returned to reopen it.
Who - based on canon (books/interviews/pottermore) - knew about the fact that Lord Voldemort was Tom Marvolo Riddle prior to Ginny being taken to the Chamber of Secrets? Obviously, Albus Dumbledore and Tom himself.
It is revealed during the series that Hagrid attended Hogwarts while Tom Riddle was also a student at the school, and that Hagrid was expelled during his third year (because Riddle, in his pre-Lord Voldemort days, framed him for opening the Chamber of Secrets).
Dumbledore knew Tom Riddle was a threat to the wizarding world: a dangerous man who needed to be stopped. But he also felt pity for him: Voldemort never had, felt, nor understood love. And in many ways, Dumbledore understood Tom: he knew what it was like to lust for power and the damage it could cause.
In the Chamber itself, we see a large statue of a wizard, which Harry presumes is Salazar Slytherin. We also meet Tom Riddle, who is, as it turns out, the heir of Slytherin.
Neither of them is Slytherin's heir. Although, as Dumbledore says, Harry's ability to speak Parseltongue is a skill accidentally transferred by Slytherin's actual heir, Voldemort, when he tried to kill Harry as a baby. So perhaps this is one myth with a bit of truth to it.
As an unqualified wizard who didn't finish his education, Hagrid was not technically allowed to perform magic. And yet, the beloved gamekeeper seemed very magical.
One fan has posited the idea that Hagrid was in fact a powerful dark wizard and Death Eater who served as a double agent for Voldemort. Yes, really. While it seems a completely outlandish idea (and even the Redditor who suggested it has said JK Rowling would not have intended it), the evidence is compelling.
Hagrid was loyal
Dumbledore has kept Hagrid working and living at Hogwarts ever since he was expelled from the school after being set up by Voldemort, which makes Hagrid grateful and loyal to Dumbledore.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
So in the course of The Chamber of Secrets, we learn that Hagrid was framed by a young Tom Riddle for opening the Chamber, resulting in Hagrid's expulsion and subsequent keeping on as groundskeeper. Some 50-odd years later, Tom (now Voldemort) attacks Hogwarts and takes Hagrid captive.
Dumbledore was the first wizard to visit Voldemort, then Tom Riddle, at his Muggle orphanage. He knew even then this was a wizard to watch – and he did, closely. When Riddle applied for the Defence Against the Dark Arts post for the second time, Dumbledore turned him down.
Her real parents were Daneel and Dean Novak, Pureblooded wizards. Turns out Daneel was Tom Riddles younger sister, Daneel Riddle. Of course, the Riddles were related to Salzar Slytherin himself, and this made Hermione the living heir of Slytherin. The problem with being a female Slytherin heir, is that they're cursed.
Harry is the Heir of Gryffindor (though his powers have been bound by his father when he was a baby), Neville is the Heir of Hufflepuff, Meghan (OFC, daughter of Sirius) is the Heir of Ravenclaw. Harry/Ginny, Ron/Hermione, Remus/Tonks.
The Heir of Hufflepuff was none other than Cedric Diggory, who was well on his way to fulfilling the prophecy of the Heir of Hufflepuff when he was tragically murdered by Peter Pettigrew.
Moaning Myrtle
Born in the late 1920s to Muggle parents, Myrtle Warren started her Hogwarts life in the early 1940s, where she was sorted into Ravenclaw.
Harry Potter came very close to being sorted into Slytherin before he persuaded the Hat to sort him into Gryffindor. Yet the spectre of Slytherin haunted him for some time afterwards, becoming particularly potent in Harry Potter and the Chamber of Secrets, when he was rumoured to be the heir of Slytherin.
Harry and Neville are both heirs of Gryffindor, as are all the other wizards who did the same throughout time.
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, Dumbledore.
Tom Senior was loved by Merope, who became obsessed enough to use a Love Potion on him. Tom M. Riddle was obsessively loved by one of his Death Eaters, Bellatrix Lestrange. Bellatrix was so eager to please him that she would 'prune' her 'family tree' by murdering her niece.
Voldemort's greatest weakness in the Harry Potter franchise was that he could never feel love.