Slytherin disliked taking students from Muggle families, seeing them as untrustworthy and unworthy of being taught magic, and tried to persuade the other founders to only take students from pure-blood families.
His viciousness to Muggle-borns is connected: Riddle may be half-blood, but Muggle-borns can claim no wizarding heritage, therefore to him they are as low as Muggles themselves. Riddle also hates Muggles because they remind him of his childhood and the Muggle father who deserted him.
Slytherin wanted Hogwarts to only accept pure blood students, when this proposal was rejected by all the other founders he became estranged and resorted to an extreme method to secure his vision for the school; murder all Muggle-borns in Hogwarts to keep the blood purity from Pure-blood wizards intact.
In some cases, wizards' hatred of Muggles is rooted in historical persecution of wizards by Muggles. Dumbledore himself comes close to allying himself with Grindelwald to subjugate Muggles because of the Muggle boys who attack and disable his sister Ariana.
While teaching at Hogwarts, Salazar and Helga Hufflepuff fell in love, however Salazar's rivalry with Godric Gryffindor brought stress upon their relationship.
The Heir of Slytherin turns out to be Ginny Weasley, who is being controlled via a magical diary that once belonged to Tom Riddle, AKA Voldemort.
Voldemort's obsession with blood purity signifies his aim to rid the wizarding world of Muggle (non-magical) heritage and to conquer both worlds, Muggle and wizarding, to achieve pure-blood dominance.
“Until the imposition of the Statute of Secrecy in 1692, the Malfoy family was active within high-born Muggle circles, and it is said that their fervent opposition to the imposition of the Statute was due, in part, to the fact that they would have to withdraw from this enjoyable sphere of social life.”
Many pure-blood families were outraged at the idea of their children using Muggle transport, which they claimed was unsafe, insanitary and demeaning; however, as the Ministry decreed that students either rode the train or did not attend school, the objections were swiftly silenced.
1. Voldemort. Tom Riddle took the core qualities of Slytherin to new heights, as he became arguably the most powerful dark wizard of all time. He learned how to split his soul and create numerous Horcruxes, thereby making himself immortal as long as the Horcruxes existed.
Godrick Gryffindor, one of the four founders of Hogwarts, and the owner of the legendary Sword of Gryffindor, was absolutely more powerful than Dumbledore— and it's a good thing he was, too, because Dumbledore wasn't around in Hogwarts' early days to keep Godrick's fellow founder Salazar Slytherin in check.
Severus Snape, Horace Slughorn, Andromeda Tonks, Narcissa Malfoy and Regulus Black were all Slytherin heroes in their own way, if you think about it. And Merlin – as in, yes, King Arthur's advisor and the most famous wizard in history – was a Slytherin.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
Because the killing curse can be blocked. In the books, Dumbledore blocks it... with Fawkes. Because when you intentionally kill someone, you destroy your own soul, then again Dumbledore is in King's Cross station just like fetus Voldemort, so maybe he's there because he actually did kill his sister.
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. Sixth year. After a rare magical illness Harry becomes outstandingly powerful.
Lucius Malfoy had a strong dislike of Albus Dumbledore. This is due to two reasons – Dumbledore believed in Muggle rights which contradicted Malfoy's pure blood beliefs. In addition, Lucius was a Death Eater, so he believed that Lord Voldemort was a much more powerful wizard than Dumbledore.
Specifically, Draco was jealous of Harry. It was easy to miss because Draco didn't often show his emotions, modelling himself on his cold, confident, calculating father, but J.K. Rowling has confirmed that a lot of his enmity towards Harry stemmed from envy.
As other people said, it is also due to the Malfoys' arrogance, the feeling of self-importance and wealth. The Weasly family is also very poor, which may also lead to a dislike with the rich, pureblood families.
Luna Lovegood is a Pureblood witch, who was sorted into Gryffindor House during Harry Potter's second year at Hogwarts School of Witchcraft & Wizardry.
In short Lord Voldemort was the sperm donor for the Lestranges as Bella's husband Rodolphus Lestrange was firing blanks. Hence why they had no child so Lord Voldemort said he would father a child with Bellatrix to help out his best deatheater friends.
At some point in time, Lord Voldemort gave Bellatrix Lestrange Hufflepuff's Cup, one of his Horcruxes, to keep safe in her vault, though he didn't tell her its true nature.
Andrea Deanisi as Wiglaf Sigurdsson, the Heir of Rowena Ravenclaw.
Myrtle's life was cut shockingly short when she was killed by the Basilisk at Tom Riddle's command.
Ginevra Molly Weasley (also known as Ginny) is the youngest child and only daughter of the Weasley family. She is Sorted into Slytherin during Harry and Jim Potter's second year.