Slytherin

"Or perhaps in Slytherin, You'll make your real friends, Those cunning folk use any means, To achieve their ends."

- The Sorting Hat

Slytherin is one of the four Houses at Hogwarts School of Witchcraft and Wizardry, and is traditionally home to students who exhibit such traits as cunning and ambition. Its emblematic animal is the snake and its colours are green and silver. Founded by Salazar Slytherin, the house is comprised mostly of pure-blood students, due to its founder's mistrust of Muggle-born witches and wizards. The house has a negative reputation, with many claiming that it is the source of most Dark Wizards in Britain, notably Tom Marvolo Riddle, a.k.a. Lord Voldemort, as well as many of his Death Eaters.

Slytherin corresponds roughly with the element of water.

Personality
"You could be great, you know, and Slytherin will help you on the way to greatness, no doubt about that."

- The Sorting Hat to Harry Potter

Slytherins tend to be ambitious, cunning, and achievement-oriented. They also have highly developed senses of self-preservation. This means that Slytherins tend to hesitate before acting, so as to weigh all possible outcomes of a decision (and how these outcomes would personally impact them), unlike Gryffindors, whose chivalrous natures would likely lead them to react immediately and instinctively.

According to Albus Dumbledore, the qualities which Salazar valued in the students he chose included cleverness, resourcefulness, determination, and "a certain disregard for the rules." Dumbledore noted that all of these were qualities possessed by Harry Potter, who was in Gryffindor.

Blood purity
The Sorting Hat claims that blood purity is a factor in selecting Slytherins. This suggests that it bases its decisions more upon the views of its members than on any accurate test of a student's lineage. Muggle-born Slytherins exist, but are very rare, as noted insultingly by Scabior the Snatcher. There have also been definite examples of half-bloods sorted into the house, including Tom Marvolo Riddle and Severus Snape. Harry Potter was nearly sorted into Slytherin, but ended up in Gryffindor instead.

Contrary to the wishes of the other founders of Hogwarts, Salazar Slytherin wanted a stricter policy of admission to the school —one limited strictly to pure-blood students. The controversy this created apparently led to Salazar leaving the school and the Chamber of Secrets behind. A millennium later, the house's students are still considered affiliated with Salazar's reputed views, and open expression of pro-blood purity sentiment does seem to be more common in Slytherin than in other Houses.

This disagreement over blood purity, which caused Salazar Slytherin's friendship with Godric Gryffindor to break, is the origin of the feud between Slytherin and Gryffindor, the two most competitive of the houses. Slytherin and Gryffindor are generally rivals in Quidditch and for the House Cup, which the former had won six years in a row prior to Harry Potter's arrival at Hogwarts in 1991. It is also rare for Slytherin and Gryffindor students to be friendly with one another, and common for them to share animosity. This was particularly the case during the First and Second Wizarding Wars; during the latter conflict, no Slytherin students joined Dumbledore's Army, which had Gryffindor, Ravenclaw, and Hufflepuff members, and some Slytherins declined to defend their school in the Battle of Hogwarts, with some joining the Death Eaters. However, there are exceptions, such as Slytherin Severus Snape and Gryffindor Lily Evans, who were best friends until Snape's use of the slur "Mudblood" and his aspirations to be a Death Eater caused Lily to sever their ties.

Reputation
"There's not a single witch or wizard who went bad who wasn't in Slytherin."

- Rubeus Hagrid to Harry Potter

It's said that most Dark Wizards were in Slytherin, though how many were from this house before Tom Marvolo Riddle began recruiting Death Eaters there is unstated. As Slytherin was his own House, it was certainly most easy for him to recruit there.

It might also be possible (though unlikely) that the Sorting Hat simply sorts anyone with ill intentions into Slytherin, regardless of whether they posess cunning and wit. Vincent Crabbe and Gregory Goyle are both incredibly stupid and lacking in wit and tact, but are still sorted into Slytherin, possibly because of their parents' affiliation with Lord Voldemort but more likely due to the "purity" of their blood.

However, it must be noted that Slytherins who oppose use of the Dark Arts and discrimination based on blood purity do exist, such as Horace Slughorn and Andromeda Black; the latter was related to many different Dark wizards and witches (most notably her sister Bellatrix Lestrange, her brother-in-law Lucius Malfoy, and her nephew Draco Malfoy), but chose to forsake the loyalty to her family in marrying the Muggle-born Ted Tonks. Also, the allegiance of Severus Snape was found to be ultimately towards Albus Dumbledore, serving as a triple agent for the Order of the Phoenix. Furthermore, there have been Dark wizards from other houses; Peter Pettigrew, who betrayed James and Lily Potter to Voldemort, was a Gryffindor.

Cunning and ambition are easily turned towards ill purposes, but are not inherently negative; furthermore, daring, intelligence, and loyalty can as easily become negative. A reason Slytherins may not be thought of as the best kind of people is because many of them seem to value their own lives more than the lives of others. When Harry was trying to run away, because he was afraid that his presence was putting his friends in danger, Phineas Nigellus saw him and said, "We Slytherins are brave, yes, but not stupid. For instance, when given the choice, we will always choose to save our own necks." There are exceptions to this rule however, such as Snape, who Harry said was a "Slytherin and...probably the bravest man I ever knew" and Regulus Black, who gave his life in an attempt to destroy one of the Horcruxes.

The truth is that while most Dark wizards are Slytherins, most Slytherins are not Dark, and smaller groups of Voldemort's supporters are aligned with other Houses. J. K. Rowling herself stated in an interview that, while all of the Slytherin students left the school before the start of the Battle of Hogwarts, several of them did return with the Hogsmeade reinforcements to join the fight against Voldemort and his Death Eaters.

Common room
The Slytherin Common room is found in the dungeons of Hogwarts Castle, and are located underneath the lake in the school grounds. Harry Potter entered the common room in his second year to find out if Draco Malfoy was the one opening the Chamber of Secrets.

Head of House
Slytherin's head of house for Harry's first six years of school was Severus Snape; however, as he fled with the Death Eaters in 1997, Potions master Horace Slughorn became the head of Slytherin House. Upon Snape's return as Headmaster later that year, he apparently approved of Slughorn's appointment, or at least did not assign any Death Eaters as a new head of house.

Translations of the name
In many translations they have changed the name:
 * Russian: Слизерин (Sleezerin)
 * French: Serpentard
 * Norweigan: Smygard
 * Finnish: Luihuinen
 * Dutch: Zwadderich
 * Portuguese (Brazil): Sonserina (taken from "Sonso" a term to someone who pretends to be innocent or harmless)
 * Czech: Zmijozel
 * Hungarian: Mardekár
 * Bulgarian: Слидерин
 * Romanian: Viperini
 * Italian: Serpeverde ("Green Serpent")
 * Slovenian: Spolzgad
 * Hindi: Nagshakti
 * Serbian: Sliterin
 * Macedonian: Змијолик (Zmijolik, which means "Snakeface")
 * Welsh: Slafenog
 * Slovak: Slizolin
 * Finnish: Luihuinen
 * The same name is used for the German, Swedish, Spanish, Danish, Turkish, Icelandic, Polish, and Portuguese (Portugal) languages.

Behind the scenes

 * The fact that J. K. Rowling intended to place a character named Mafalda, a half-blood who was the daughter of a Squib and a Muggle, in Slytherin, suggests that Rowling at least does not view the Slytherin House desire for blood-purity as particularly influential upon the Sorting Hat. Mafalda was intended to be a relative of the Weasley family.
 * Slytherin students might possess a certain skill in Potions. Harry's two Potions masters, Severus Snape and Horace Slughorn, both belonged to the Slytherin house. However, it is possible that this talent in Slytherin students could merely be a coincidence, as students from other houses at Hogwarts also shared this talent, such as Harry Potter's mother, Lily Potter (nee Evans). This is shown through Slughorn's many references to her skill in the subject throughout most of Harry Potter and the Half-Blood Prince.
 * Slytherin students also seem to be gifted in Occlumency. Most of the known Occlumens in the book come from Slytherin (namely Lord Voldemort, Severus Snape, Bellatrix Lestrange, Draco Malfoy, and Horace Slughorn).
 * Most Legilimens in the series also come from Slytherin house (namely Voldemort, Snape, and Bellatrix), which means that Legilimency is another skill that Slytherin students are gifted in.

Notes and references
Slytherin Serpentard Slytherin Слизерин Smygard