Serpent of Slytherin

"...That is believed to be some sort of monster..."

- Professor Binns on the Chamber of Secrets' occupant

The Serpent of Slytherin was a basilisk placed by Salazar Slytherin inside the Chamber of Secrets at Hogwarts School of Witchcraft and Wizardry. The basilisk could only be controlled by Slytherin's one true heir, Tom Riddle. This means that despite it being a snake, other Parselmouths (such as Harry Potter) have no control over it.

First Opening of the Chamber of Secrets
Salazar Slytherin's basilisk was born in the chamber, as revealed by Aragog. In the early 1940s, the Chamber of Secrets was opened by a Slytherin fifth year, Tom Marvolo Riddle, who was able to control the creature through his status as the heir of Slytherin. Riddle unleashed the basilisk on the school, his goal being to rid the school of Muggle-born students. All the victims were merely Petrified, except for a student named Myrtle, who was killed in the girls' bathroom on the first floor. A sink in this bathroom concealed the entrance to the Chamber of Secrets. These events were nearly the cause for the permanent closing of Hogwarts.

To avoid this undesirable consequence for Hogwarts, which was the closest thing he had to a home, Riddle framed Gryffindor third year Rubeus Hagrid for all the events, claiming Hagrid's pet Acromantula Aragog was responsible for the attacks. Hagrid was expelled, and the attacks stopped. However, Transfiguration teacher Albus Dumbledore became suspicious of Riddle, and thus prevented him from further terrorising the school, since Riddle now feared discovery. Dumbledore also convinced Professor Armando Dippet, who was Headmaster at that time, to allow Hagrid to stay at Hogwarts as gamekeeper.

Second Opening of the Chamber of Secrets
Slytherin's basilisk would only listen to Tom Marvolo Riddle (later Lord Voldemort), regardless of Harry Potter being able to understand and speak Parseltongue to it in the Chamber of Secrets. It is possible that the basilisk was trained, enchanted, or persuaded to obey only the Heir of Slytherin, and not all Parselmouths.

Fifty years after Tom Riddle's original attack on Hogwarts, the basilisk was re-awakened by a shade of Riddle generated by a Horcrux he had housed in his old diary. This shade possessed Ginny Weasley after Lucius Malfoy slipped the diary into her cauldron during a confrontation in Flourish & Blotts, as part of his plan to discredit her father. However, although Riddle/Ginny killed the Hogwarts roosters to prevent them being used against the basilisk, the basilisk managed only to petrify a few students, a ghost, and a cat, each of them seeing only the snake's reflection or seeing it through something, rather than looking upon the snake directly. Using his own ability as a Parselmouth, Harry was able to hear the basilisk and attemped to find her. Later in their search Hermione became one of the basilisk's victims, but she had already managed to get some information on the basilisk for Harry and Ron, information which they found still clutched in her Petrified hand. Harry and Ron (accompanied by a reluctant Gilderoy Lockhart) entered the Chamber of Secrets, where Ginny Weasley was being held by Tom Riddle. After being separated from Ron and the self-Obliviated Lockhart, a battle commenced between Harry Potter and the basilisk.

Battle with Harry Potter and death


During the battle between Harry Potter and the basilisk, Dumbledore's phoenix Fawkes was able to blind the basilisk, allowing Harry to fight the basilisk without the fear of being killed instantly by its gaze. During that period of hiding, Harry obtained Godric Gryffindor's sword from the Sorting Hat, which had been brought to him by Fawkes. Harry stabbed the basilisk through the roof of its mouth, killing it. Harry subsequently used one of the creature's fangs to destroy Tom Riddle's diary, which he would later discover was one of Voldemort's seven Horcruxes.

Post-mortem
By 1998 the basilisk's body had fully decomposed, leaving just a skeleton. Another one of the basilisk's fangs was used once again by Hermione Granger to destroy another Horcrux, Helga Hufflepuff's cup. The fang's venom, which was absorbed by the sword that slew it due to its taking in only that which made it stronger, allowed it to destroy Slytherin's locket. While the sword slew Nagini, due to her being a living creature, it's unknown whether or not any sword would have done the job.

Traits
A horrifying monster with dark green scales, this creature was immensely large and had deep yellow eyes. It possessed great strength, and as a basilisk, it could kill with a gaze, and petrify with an indirect look. In addition, its fangs were capable of destroying Horcruxes. It could breathe while submerged underwater. Although it was rendered blind by Fawkes, Harry Potter was its eventual killer.

Known victims
The following list shows all known Basilisk victims both killed, Petrified, and otherwise harmed by the monster.

Killed

 * Moaning Myrtle
 * Postmortem: fangs and venom destroyed two pieces of Tom Riddle's soul (in Tom Riddle's Diary in 1993 and Helga Hufflepuff's Cup in 1998.)
 * Indirectly: Godric Gryffindor's Sword which is imbibed with a Basilisk's venom, destroyed Salazar Slytherin's Locket and Marvolo Gaunt's Ring, both of which contained a piece of Tom's soul.
 * The sword also slew Nagini, though the venom may not have been necessary to release the soul, due to the instability of living Horcruxes.
 * In the film version, a fang is also used to stab Rowena Ravenclaw's Diadem before it is engulfed by Fiendfyre.

Petrified

 * Several unknown students during 1943
 * Mrs. Norris (saw its reflection in puddle of water)
 * Colin Creevey (saw through lens of camera)
 * Justin Finch-Fletchley (saw through Nearly Headless Nick)
 * Nearly Headless Nick (made eye contact, but was a ghost, and could not die again)
 * Hermione Granger (saw in Penelope's mirror)
 * Penelope Clearwater (saw in her mirror)

Injuries

 * Harry Potter (her fang went into Harry's arm, who would have died if not healed by Fawkes)

Behind the scenes

 * In LEGO Harry Potter: Years 1-4, Harry does not get pierced by the Basilisk's fang and instead pulls it out of the dead Basilisk's mouth. Also, the basilisk notices Harry when Ginny screams at one of his disembodied eyes. A third difference is that the basilisk has a scarlet plume on its head, thus its gender is male. Additionally, Ginny helps Harry during the battle as opposed to being unconscious the whole time.
 * Penelope Clearwater is the only victim of the 1992–1993 school year incident who was not a victim of Slytherin's basilisk in the film adaptation of Harry Potter and the Chamber of Secrets. Still, there was a mirror next to Hermione's bed, but it is never mentioned that Penelope was with Hermione.
 * In the film adaptation of Harry Potter and the Deathly Hallows, when Ron and Hermione enter the Chamber of Secrets, the skeleton of the basilisk is still there, but appears to be in a different spot than where Harry killed it earlier. Additionally, the fang which had been lost in Harry's arm appears to still be in the mouth of the skeleton.
 * In recalling his father reading the first two Harry Potter books to him, Daniel Radcliffe stated that his father had a great voice for the basilisk. He suggested his father to director Chris Columbus, and his father was mortified.

Appearances

 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Chamber of Secrets (film)
 * Harry Potter and the Chamber of Secrets (video game)
 * Harry Potter and the Prisoner of Azkaban
 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (film)
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 1
 * Harry Potter and the Deathly Hallows: Part 1 (video game)
 * Harry Potter and the Deathly Hallows: Part 2
 * LEGO Harry Potter: Years 1-4
 * LEGO Harry Potter: Years 5-7 
 * LEGO Creator: Harry Potter and the Chamber of Secrets
 * Harry Potter LEGO Sets
 * Harry Potter Trading Card Game

Notes and references
Basilisco di Salazar Serpeverde