Each of the four Hogwarts houses has its own ghost. Slytherin boasts the Bloody Baron, who is covered in silver bloodstains.
Six ghosts are specifically named in the books: the four House ghosts (Nearly Headless Nick of Gryffindor House, the Fat Friar of Hufflepuff House, the Grey Lady of Ravenclaw House, the Bloody Baron of Slytherin House); Professor Binns, the History of Magic teacher; and Moaning Myrtle.
The Fat Friar is the ghost of Hufflepuff house. He is a portly, jolly spirit in clergyman's garb. Not much is known about him.
Born Helena Ravenclaw, she was a witch and daughter of one of Hogwarts' founders, Rowena Ravenclaw. Helena turned into the ghost known as the Grey Lady after she was brutally murdered by the Bloody Baron. The character was portrayed by actress Kelly MacDonald in Harry Potter and the Deathly Hallows – Part 2.
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.
1 Rowena Ravenclaw
As one of the most famous Ravenclaws, Rowena built her house on the ideals she valued and embodied — intelligence and creativity.
The Riddle House was a manor house in Little Hangleton that was home to Thomas, Mary, and Tom Riddle Senior (Lord Voldemort's paternal family). Their mansion was perched atop a hill overlooking the village. Tom Riddle (Lord Voldemort) murdered his grandparents and father in the Riddle House in 1943.
The Head of Slytherin is Horace Slughorn (who left the role to Severus Snape for fifteen years before taking it up again in 1996) and the House's patron ghost is the Bloody Baron.
Unfortunately, that man was the Bloody Baron, who was head over heels with Helena, and stabbed her in a rage when she refused to come home. After Helena was tragically killed, legend tells us that Rowena Ravenclaw died of a broken heart.
When her mother sent The Bloody Baron to bring her home, instead, he fell in love with her, then murdered her when she did not return his feelings. Helena would go on to haunt Hogwarts forever more, going by the name of The Grey Lady.
The History of Magic teacher for the entire series, Cuthbert Binns has the distinction of being the only teacher at Hogwarts who is a ghost.
Unknown date, 1946: Tom Riddle murders Hepzibah Smith, sending a piece of his soul into Helga Hufflepuff's cup. It becomes the third Horcrux. (Riddle also steals the Slytherin locket.)
In the world of Harry Potter as we know it, there are no recorded instances of a person who was sorted into Hufflepuff ever becoming a Death Eater, or any other kind of Dark Wizard for that matter.
Moaning Myrtle, born as Myrtle Elizabeth Warren, was a former Ravenclaw student (now a ghost) who haunts the girl's bathroom on the first floor (called the second floor in the US editions of the book) of Hogwarts School of Witchcraft and Wizardry.
Although they surely would have done whatever possible to remain in Harry's life, they had no reservations about giving up their own to save him from Voldemort. Since they demonstrated a lack of fear of death, they were immediately less likely to become ghosts.
3 The Grey Lady
Fans remember Helena Ravenclaw as the shy if somewhat capricious ghost that aided Harry in finding her mother's diadem. Just like in Harry Potter, in Hogwarts Legacy, The Grey Lady is reclusive and somewhat fragile. Ravenclaw players can find her in their halls, where she can be seen and heard crying.
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.
Salazar married a witch named Nerezza of Aosta. They had two children: Maximiliana Slytherin Argent and Cenric Slytherin. Salazar Slytherin founded Hogwarts School of Witchcraft and Wizardry with Rowena Ravenclaw, Helga Hufflepuff, and Godric Gryffindor in approximately 993 A.D.
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.
At Hogwarts, she, along with her sisters, was sorted into Slytherin. It is suggested in the novels that, as a student, Bellatrix associated with a group of students – including Rodolphus Lestrange, Severus Snape, Avery, Evan Rosier and Wilkes – who nearly all became Death Eaters.
Delphini (b. March 1998), known by the nickname Delphi, was a British half-blood Dark witch, the daughter of Tom Riddle and Bellatrix Lestrange. Being the only child of Lord Voldemort, she was able to speak Parseltongue, and she became the only known living heir of Salazar Slytherin after the demise of her father.
The most likely reason why Lord Voldemort's nose disappeared and he devolved into such an evil-looking creature is that as he dabbled deeper into the Dark Arts, his appearance gradually became as distorted as what remained of his twisted soul.