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She lived in the Chamber of Secrets until Ginny Weasley (possessed by part of Tom Riddle's soul contained in his Diary) opened the Chamber of Secrets. The Basilisk escaped inside the school and petrified a few people which included Filch's cat Mrs. Norris, Colin Creevey, Justin Finch-Fletchley, Nearly Headless Nick, Hermione Granger and Penelope Clearwater since they witnessed the monster and did not make direct eye contact.
Of the many fearsome beasts and monsters that roam our land, there is none more curious or more deadly than the Basilisk, known also as the King of Serpents. This snake, which may reach gigantic size and live many hundreds of years, is born from a chicken’s egg, hatched beneath a toad. Its methods of killing are most wondrous, for aside from its deadly and venomous fangs, the Basilisk has a murderous stare, and all who are fixed with the beam of its eye shall suffer instant death. Spiders flee before the Basilisk, for it is their mortal enemy, and the Basilisk flees only from the crowing of the rooster, which is fatal to it.
~ Harry Potter, reading information on the Basilisk.
The first member of these creatures was created in ancient Greece by Herpo the Foul and was one of the first examples of the Dark Arts and was considered highly dangerous, inhumane and illegal to breed. The Basilisk was considered the enemy of almost everything, the enemy of humans, spiders, and roosters. The Basilisk was especially feared by spiders, with them even fearing to name it, presumably because of their eight-eye vision which would render them vulnerable to paralysis.
The Medieval Period
There were no recorded sightings of Basilisks, but Slytherin himself bred a Basilisk deep within Hogwarts castle, marking the beginning of the Basilisk's reign of terror in the school. The Basilisk lived for two hundred years, unless killed, and she posed a serious threat, which would be seen in the twelfth century.
Harry Potter: But if you're not the monster, then what did kill that girl 50 years ago? Aragog: We do not speak of it! It is an ancient creature we spiders fear above all others.
~ Harry Potter and Aragog about the Basilisk.
The beast was summoned up by Slytherin's heir, Tom Marvolo Riddle, in 1943, to continue her original purpose and purge Hogwarts of those "unworthy to attend" (Muggle-Borns). She petrified many students and ended up killing one girl (Moaning Myrtle), sending the school into a panic and threatening its closure. To prevent his beloved Hogwarts from closing, Riddle called off the snake and framed Rubeus Hagrid and his illegal pet, Aragog the Acromantula, as the ones responsible. The Basilisk was sent to slumber once more within the recesses of the Chamber.
Fifty years later, the monster was awoken once more to finish the job after Riddle's shade from the Diary possessed Ginny Weasley and used her to open the Chamber of Secrets. The school roosters were killed by Ginny to prevent them from interfering with the Basilisk's mission, and attacks on many students (as well as Filch's cat and one of the school ghosts) sprung up. Several signs pointed to the Basilisk as the culprit, with most victims petrified, the roosters dead, spiders fleeing from the school, and Harry Potter hearing threatening voices within the walls (as the Basilisk used the plumbing system to travel from place to place). Harry was thought to be responsible for the release of Slytherin's Monster event because he could speak Parseltongue, the language of snakes; an ability shared by Voldemort and the great Salazar Slytherin. When Hermione Granger became petrified, everyone else started to think otherwise because she was one of Harry's best friends. Harry and Ron went to the spider Aragog, who told them that it was not him who was the monster in the Chamber of Secrets, and informed them of the "unspeakable horror" living in the depths of the school. Harry and Ron then visited Moaning Myrtle, who was actually the girl that the Basilisk had killed the first time that she was let out of the Chamber. She told them that she had seen a pair of "great yellow eyes" beside one of the sinks in the girls' lavatory.
Harry and Ron investigated and found a small snake engraved on the side of a sink, hinting at the location of the entrance to the Chamber of Secrets; Harry figured that he had to speak in Parseltongue in order to access the Chamber portal, which turned out to be a large pipe that led directly under the school and the lake. Harry was able to slay the Basilisk (with help from Fawkes the Phoenix and the Sword of Godric Gryffindor) and save Ginny from Riddle, who turned out to be a part of Voldemort's soul encased in the Diary.
Later, in 1998, Ron and Hermione were able to reenter the Chamber of Secrets (with Ron providing a surprisingly good imitation of Parseltongue needed to open the sink) to collect fangs from the Basilisk's skeleton, which they used to help Harry destroy Voldemort's Horcruxes.
Parseltongue won't save you now, Potter! It only obeys me!
~ Tom Riddle, explaining the Basilisk's complete loyalty to the Slytherin bloodline.
Basilisks are always violent, sadistic, and bloodthirsty beasts. Although it can be inferred that these serpents are instinctive at very least in the wild, it is obvious they can develop distinct personality depending on their upbringing. This is best shown in the case of a most well known of basilisk, the Serpent of Slytherin; in addition of natural sadism and ferocity of her race (which reflected through things she said while Harry listened to her attacking her victims), she displayed blind and unshakable devotion to the Heir of Slytherin, Lord Voldemort, along with nerves of steel to the boot, proving greater malice than her brethren. Given that Salazar was the one who bred her, it made sense that the aforementioned devotion was the result of her either trained, enchanted or persuaded to obey only the Heir of Slytherin and not all Parselmouths.
Ron Weasley: But if it kills by looking people in the eye, why is that no one's dead? Harry Potter: Because no one did look it in the eye. Not directly at least.
~ Harry and Ron discussing why no one has been killed by the Basilisk.
Several unknown students attending Hogwarts in 1943 (all petrified, possibly restored).
Myrtle "Moaning Myrtle" Warren (died, became a ghost) (the only victim who died).
Mrs. Norris (petrified, restored to health) (looked at her reflection in the water of the floor)
Colin Creevey (petrified, restored) (saw her through his camera)
Sir Nicholas "Nearly Headless Nick" de Mimsy-Porpington (petrified, restored though already a ghost)
Justin Finch-Fletchley (petrified, restored). (looked at her through Nick)
Penelope Clearwater (petrified, restored). (saw her in her mirror)
Hermione Granger (petrified, restored). (saw her in Penelope's mirror)
Concept art of the Basilisk.
The Basilisk with Tom Riddle.
The Basilisk's evil grin as she prepares to kill Harry.
The Basilisk in Lego form. (Note: the red plume on her head, making her male; the Basilisk in canon is female)
Funko POP figure of the Basilisk.
Salazar Slytherin's Basilisk in the book and film is a Female. Male Basilisks have a red plume of feathers on their heads.
In LEGO Harry Potter: Years 1-4, the Basilisk is male because it has a red plume on its head.
In the film, Penelope Clearwater was not shown as a victim of the Basilisk.
Daniel Radcliffe suggested to director Chris Columbus that his father be cast as the voice of the Basilisk in the film, recalling that he gave the Basilisk 'a great voice' when he read his son the first two books. Radcliffe's father was reportedly mortified by the suggestion.
The Basilisk in the film was a mix between CGI technology and an animatronic puppet. Twenty feet of the creature and the head were built in the studio for close-up shots of the snake.
The Basilisk's corpse can be seen inside the Chamber during the Harry Potter and the Forbidden Journey attraction at the Wizarding World of Harry Potter in Orlando, Florida.
In Jimmy Neutron, Finbarr Calamitous made a robot based off the Basilisk when Jimmy is playing a Harry Potter-based character and Carl playing a character based on both Quirinus Quirrell and Tom Riddle (with the former being a vessel for Voldemort and the later being an incarnation of Voldemort).
Ironically, the Basilisk that Voldemort used to purge Hogwarts of Muggle-Borns and Harry Potter was used against him by having her venom destroy most of his Horcruxes, which eventually led to his death.
In addition to a rooster's crow, the smell of a weasel is also unbearable and practically fatal to a Basilisk in mythology.