Professor Salazar Slytherin was a wizard of Medieval times. He was a parselmouth (a wizard with the rare ability to speak with snakes). He was one of the four founders of Hogwarts School of Witchcraft and Wizardry. As he didn't trust muggle-born students, he expressed his opinion not to accept them at Hogwarts. However, when the other founders didn't agree, Slytherin left the school and did not return again, but not before creating the Chamber of Secrets and concealing a basilisk inside. It is unknown when he died. Slytherin House is named after him.
 First Book
The Sorting Hat described him as "power hungry Slytherin," and that he came "from a fen." A fen is a marshland, typically inhabited by water fowl, amphibians and snakes. This could be the reason why he and his family have the rare gift of speaking Parseltongue. The Fens of Eastern England are in Norfolk, Lincolnshire, Cambridgeshire and adjoining counties, although it is not established that Slytherin actually came from that particular region.
 Second Book
Like Rowena Ravenclaw and Godric Gryffindor, Salazar Slytherin appears to have carefully selected members of his House. According to Albus Dumbledore, the qualities which Slytherin prized in his "handpicked students" included resourcefulness, determination, and a certain disregard for the rules, along with the ability to speak Parseltongue. He also selected his students according to cunning, ambition, and Blood purity.
After founding Hogwarts and co-existing for years, a rift eventually began to grow between Slytherin and the other founders. Slytherin despised taking students from Muggle families, seeing them as untrustworthy, and tried to persuade the other founders to only take students from pure-blood families. However, the other founders didn't agree with Slytherin, particularly Gryffindor. Eventually, Slytherin and Gryffindor had a huge argument over the subject, and the end result was that Slytherin chose to leave the school . It is unknown when he died.
According to ancient legend, as told by History of Magic Professor Cuthbert Binns, Salazar Slytherin was responsible for the construction of the Chamber of Secrets beneath Hogwarts dungeons. It was specifically created for the purpose of purging the school of all Muggle-born students. The Chamber contained a Basilisk which could be controlled only by his own "true heir", and use it to rid the school of all Muggle-borns. At least part of the legend was revealed to be true in 1943, when Tom Marvolo Riddle, the heir of Slytherin, opened the Chamber and used the Basilisk to attack Muggle-borns. One girl he actually killed is now a ghost known by the name Moaning Myrtle. The opening to the Chamber of Secrets is located in the bathroom she now haunts, and can only be opened by speaking Parselmouth as Slytherin could. Riddle opened the Chamber again in 1993 through the use of one of his seven Horcruxes, his diary. Using the bit of his soul encompassed by the diary, he possessed Ginny Weasley and forced her to do his bidding. However, this second time opening the Chamber Riddle seemed to have a slightly different goal than the first time. For example, Ginny is a pure-blood witch, but he did not care. While he still attacked Muggle-born students, ultimately, his goal was to lure Harry Potter into the Chamber and kill him.
 Outward Appearance
The statue of Salazar Slytherin in the Chamber of Secrets depicts an "ancient and monkey-like" man with a "long thin beard that fell almost to the bottom of his sweeping robes." His beard was white in colour. Marvolo Gaunt, a blood relative, is similarly described as being monkey-like in appearance.
 Magical abilities and skills
- Parselmouth: Salazar Slytherin was one of the earliest recorded Parselmouth and used this ability to control a Basilisk. His house's symbol is a serpent due to this, and he passed this trait on to his descendants.
- Basilisk breeder: Slytherin managed to breed a Basilisk and kept it alive in the Chamber of Secrets for over one-thousand years, surpassing its average nine-hundred years lifespan.
Salazar Slytherin owned a locket emblazoned with the letter S that became a heirloom of his last known line of descendants, the Gaunts. Merope Gaunt sold the locket to Caractacus Burke. It was then bought up by Hepzibah Smith, who had a love for antiques. It was subsequently stolen from her by Tom Marvolo Riddle. Riddle would later turn the locket into a Horcrux, and conceal it in a seaside cave he had visited in his youth. The same locket was later removed from the cave by Regulus Black with aid from his house-elf, Kreacher. Kreacher was ordered to destroy the locket, but was unable to do so.
It was later stolen from the Black family home at 12 Grimmauld Place by Mundungus Fletcher, and eventually found its way into the hands of the Ministry of Magic employee, Dolores Umbridge. Umbridge used it as an intimidation tool by wearing it and claiming the S stood for Selwyn, a pure-blood family line. She either did not know better or wanted to conceal its real meaning from the public.
The locket was recovered by Harry Potter, and was later destroyed by Ron Weasley with Godric Gryffindor's Sword. The act of destruction removed all of the Horcrux's power.
The name Salazar is originally a Portuguese family name. António de Oliveira Salazar was a fascist dictator of Portugal (where Rowling lived for several years) from 1932 to 1968. Rowling stated that the name "Salazar Slytherin" was chosen after the Portuguese dictator's name. Meanwhile, Slytherin may refer to the words "sly" as well as "slithering", which is the form of locomotion of snakes, possibly referring to his rare ability to talk to snakes called parseltongue. Salazar, sometimes spelled as Salasar, is a Basque surname meaning old hall (from Castilian Sala (hall) and Basque zahar (old)). The name originates from the town of the same name: Salazar, in northern Burgos, Castile
Harry is very distantly related to Salazar Slytherin, but is not a descendant of him, as Voldemort is descended from Slytherin and the second Peverell brother while Harry is a descendant of the third.
 Additional Canon
 Video Game
There were also portraits of Slytherin hung at Hogwarts Castle, one guarding a secret shortcut between the dungeons antechamber and the Entrance Hall side room. The password required to gain access to said shortcut was Mortal Dread. The other was hung at the Headmaster's office, part of the Headmaster portraits gallery
 The Films
- On the DVD of Harry Potter and the Chamber of Secrets (film), Slytherin's portrait is seen in the headmaster's office, although he was never headmaster
- In the film, the statue of Salazar Slytherin only covers his head, compared to the book where it was full-body.
 J. K. Rowling's Official Website
- Slytherin was the featured "Wizard of the Month" for June 2007 on J. K. Rowling's website, where he was profiled thus: "One of the four celebrated Founders of Hogwarts School of Witchcraft and Wizardry, Salazar Slytherin was one of the first recorded Parselmouths, an accomplished Legilimens, and a notorious champion of pure-blood supremacy."
- Both pictures of Slytherin in the Wizard of the Month and at the Famous Cards depict Slytherin with steepled fingers.
 Wizarding World of Harry Potter
- Salazar Slytherin appears as a portrait in the "Forbidden Journey" ride at Universal Orlando.
- Harry Potter and the Philosopher's Stone (video game) (Appears on a Famous Wizard Card)
- Harry Potter and the Chamber of Secrets (First mentioned)
- Harry Potter and the Chamber of Secrets (film) (Portrait)
- Harry Potter and the Chamber of Secrets (video game) (Mentioned only) (Appears on a Famous Wizard Card)
- Harry Potter and the Half-Blood Prince (Mentioned only)
- Harry Potter and the Half-Blood Prince (film) (Portrait)
- Harry Potter and the Deathly Hallows (Mentioned only)
- The Wizarding World of Harry Potter
- Wizard of the Month