|Nội dung||Large size, serpentine, carnivorous, poisonous|
|Xuất hiện lần đầu||Harry Potter and the Chamber of Secrets|
A Basilisk — otherwise known as the King of Serpents — is a bright green snake, which can grow to an enormous size. It is a rare, wizard-bred creature, born from a chicken egg hatched beneath a toad; the creation of them is illegal and falls under the Ban on Experimental Breeding. Males are distinguishable from females by the bright red plume on their foreheads. Basilisks have long, poisonous fangs and shed their skin at intervals.
If someone looks directly into the Basilisk's bulbous yellow eyes, then he or she will die instantly as Moaning Myrtle did, as mentioned in Harry Potter and the Chamber of Secrets. If someone looks indirectly (in a reflection, through the lens of a camera), he or she will become Petrified.
A rooster's crow is fatal to Basilisks. Spiders, including Acromantulae, are terrified of them and flee from them.
In Harry Potter and the Chamber of Secrets, a Basilisk which lives in the Chamber of Secrets is released periodically by the Heir of Slytherin. The Heir, whose control over the Basilisk is not complete, attempts to guide it to attack students who are Muggle-born. This is apparently an attempt to extend Salazar Slytherin's preferred policy for admittance into the school. Slytherin, one of the four Founders of Hogwarts, believed that only the children of wizards ought to be accepted, and departed the school when the other three would not agree with him. Several students of varying parentage and one cat, Mrs Norris, are Petrified by the Basilisk. When Harry enters the Chamber and fights the blinded Basilisk, he thrusts a sword into the roof of its mouth, a move that will kill it; in turn, one of its fangs pierces Harry's arm, the poison of which nearly kills him.
The monster in the Chamber of Secrets, in Harry Potter and the Chamber of Secrets is a Basilisk. The process of discovering this is a slow one, both for the reader and for the Trio. The first clue, which happens barely a week in to the term, is the disembodied voice that Harry alone can hear when he is doing his detention with Professor Lockhart. In retrospect, it becomes obvious that Harry can understand it because he is a Parselmouth and can understand snake language; to Lockhart, and to anyone else in the vicinity, what Harry hears as a voice is only a low hissing and sizzling sort of noise. As the Trio leave Nearly Headless Nick's Deathday party, the voice seems to be proceeding upwards between floors without benefit of stairs or anything else; while we have been misled so far into believing that this voice may be coming from something without a physical body, in retrospect again it becomes obvious that the creature is travelling through the pipes. The Petrification of Mrs Norris is another clue, and the dead roosters that Hagrid is waving about at the time Justin Finch-Fletchley and Nearly Headless Nick are Petrified, is of course a final clue. While much is made in the story of the fact that spiders fear Basilisks, to the point that Aragog will not speak its name, this may be an addition to the Basilisk legend by the author; as such, it is a clue for the Trio, specifically for Hermione, but not necessarily for the reader.
Basilisks are impossible to control, except by Parselmouths. A Basilisk would be a dangerous servant, as even its master cannot look into its eyes. As such, they do not play much further part in the story; while it's certainly true that Voldemort can control them, even under that control they would prove as dangerous to his allies as to his enemies.
- The one Basilisk that we witness has lived for a thousand years in the Chamber of Secrets, and has apparently become very large. What would it have eaten, locked in the Chamber? How did the animals that it apparently ate, based on the skeletons that Harry found himself walking on, get past the outer door of the Chamber?
- The Basilisk has done all of Voldemort's bidding. How come Harry can't control it?
The major story arc of the series revolves around Horcruxes, magical items which are not defined until late in the sixth book. At that time, we will learn that it is necessary to destroy Voldemort's Horcruxes before Voldemort himself can be defeated. We also learn that one of the Horcruxes, Tom Riddle's diary, was destroyed by Harry's stabbing it with a Basilisk fang.
Later still, we learn that in fact Basilisk venom is one of the very few things that can destroy a Horcrux. We learn also that the Sword of Gryffindor had been used to destroy one, the Gaunt ring. This sword, being Goblin-made, will absorb anything that will strengthen it, had apparently absorbed Basilisk venom in the battle against the Basilisk in the Chamber of Secrets, and so now can be used to destroy Horcruxes. It is, in fact, used to destroy two more, Slytherin's locket and Nagini, and Helga Hufflepuff's cup, another Horcrux, is destroyed by the remaining venom in the Basilisk's fangs still lying around in the Chamber of Secrets five years later.
The question of what the Basilisk eats is not entirely idle. We see that the Chamber of Secrets has two doors, the basin in Moaning Myrtle's washroom and the inner door, both of which open on a Parseltongue command. Because the shed skin and the skeletal remains are outside the inner door, we must assume that the Basilisk can open it, and in fact has been, in order to hunt. We must assume that the Chamber cannot be opened from inside by the Basilisk, else it would have been hunting through the school proper for centuries — it was, after all, placed in the Chamber on Salazar Slytherin's departure, possibly a thousand years before Tom Riddle re-opened the Chamber. By the same token, we cannot assume that it has access to the Lake, as if there was a way to reach the Lake, the Basilisk would have likely used it to leave the Chamber for the outside of the Castle and hunt for more interesting game. So, it will have been hunting through the Hogwarts plumbing all those years. Why then has Harry not heard it before? We can only speculate. Perhaps, with the Chamber entrance closed, the pipes it can reach are limited; it is, after all, quite a large snake. We cannot assume that anyone has been feeding it; the Chamber remained closed and hidden for the millennium between Slytherin's departure and Riddle's arrival, and even for a magical being, a thousand years without food is a long time.