Basilisk

"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."

- A page from an old library book.

The Basilisk is a giant serpent, also known as the King of Serpents. It is a creature bred by Dark Wizards. Herpo the Foul was the first to breed a Basilisk; he accomplished this by hatching a chicken egg beneath a toad which resulted in the creature known as a Basilisk. Basilisk breeding was banned in Medieval times. The practice can be hidden when the Department for Regulation and Control of Magical Creatures comes to check by simply removing the egg from the toad.

Although classified as an XXXXX creature, meaning it is a known wizard-killer that cannot be domesticated due to its immense powers, because the Basilisk is still a serpent, a Parselmouth may place a Basilisk under his or her control. This depends on the relationship between the Basilisk and the Parselmouth, as Tom Riddle, alias Lord Voldemort, was the only one who could command Salazar Slytherin's Basilisk, while Harry Potter had no control over it.

Traits
The Basilisk can grow up to fifty feet in length, and is a dark green colour with large yellow eyes. These eyes have the power to instantly kill anyone who looks into them. If the victim looks indirectly at the Basilisk's eyes, such as its reflection, they will merely become Petrified, as was the case with Hermione Granger and Colin Creevey, however Myrtle (commonly known as Moaning Myrtle) was not so fortunate, and looked directly into the Basilisk's eyes, which resulted in her dying immediately. Another way of surviving a Basilisk's gaze is by seeing it through another object. Another example mentioned above was when Colin Creevey saw it through his camera, resulting in his petrification and his camera lens becoming melted. Justin Finch-Fletchley saw the Basilisk through the translucent Nearly-Headless-Nick, and both were petrified. Sir Nicholas, being a ghost, was already dead; as such, he only became Petrified as well, although he did look at the beast's eyes directly. It is also known for its ability to squeeze itself through pipes. This petrification seems quite powerful, as even the Elder Wand-wielding Dumbledore concluded that the only way to reverse the effect was through the use of Mandrake Restorative Draughts.

Phoenixes are immune to this deadly gaze, although spiders, such as Aragog and his ever-growing clan, are terrified of the Basilisk, and describe it as their enemy, refusing to even speak of it or mention its name.

The Basilisk's sharp fangs are full of deadly venom, powerful enough to kill a human in a matter of minutes; Phoenix tears are the only known cure. It can also damage inanimate objects so thoroughly that they are impossible to restore, and thus it is one of the few substances powerful enough to destroy a Horcrux. The venom is potent even long after death. Basilisk skin is armoured like that of a dragon's, which deflects spells cast upon it. The Basilisk sheds its skin at intervals, like all other snakes, when it grows.

Basilisks can live a natural life of at least nine hundred years, though Salazar Slytherin's Basilisk lived for approximately a thousand years. This is accomplished by using Parseltongue to put the creature into a deep sleep that prevents it from aging, similar to suspended animation. Their mortal weakness is the crowing of a rooster. Basilisks feed off vertebrate animals. The male can be distinguished from the female by a single scarlet plume on its head.

Muggle myth
In mythology, a Basilisk is depicted four ways: a huge lizard, a giant snake, a three-foot high rooster with a snake's tail and teeth (also known as a cockatrice), and a shape-shifting dragon. Every new version of the Basilisk in a story added to its deadly array of weapons, such as accounts of fire-breathing and the instantaneous killing power of its call. In the mythology, the basilisk had three weaknesses: a weasel, the crowing of a rooster, or the sight of its own reflection.

Muggles of course do not believe the Basilisk to be real. Another creature named the Common basilisk (Basiliscus basiliscus) is a small lizard that has no magical powers or properties, although it can run on water for short distances.

Basilisk's venom
Basilisk venom is an extremely poisonous substance that only has one known cure: phoenix tears. Basilisk venom is so powerful that it can kill a person within minutes, making the person drowsy and blurry-visioned before they die. It has a very long lasting effect which still remains potent even up to five years or more after the snake has died. The venom is one of the very rare few known substances that can destroy Horcruxes.

When Harry Potter slew Salazar Slytherin's Basilisk with Godric Gryffindor's Sword in 1993, the sword became imbued with the basilisk's venom, giving it the ability to destroy Horcruxes.

Basilisk egg
A Basilisk egg is the egg of said creature. They are chicken eggs hatched beneath a toad, thus creating the deadly King of Serpents. This method was first discovered by Herpo the Foul, in Ancient Greece, and has been banned since medieval times.

Etymology
The Ancient Greek basil(eus) means "king", with the suffix -iskos being a diminutive, the whole having the sense of "princeling" or the like, purportedly for the crown-like white spot on its head.

Behind the scenes

 * According to Igor Karkaroff, Alastor Moody has smashed apart a birthday present that he thought in paranoia was a cleverly disguised basilisk egg before finding out it was a carriage clock.
 * The basilisk is often confused with the cockatrice, but the basilisk is born from a chicken’s egg hatched beneath a toad, while the cockatrice is hatched by a chicken's egg incubated by a serpent. The cockatrice is also usually depicted with wings, while the basilisk is not.
 * Although an average basilisk is said to have an average lifespan of 900 years Salazar Slytherin's Basilisk lived for approximately 1000 years, being there since Slytherin built the Chamber of Secrets around that time.
 * In LEGO Harry Potter: Years 1-4, the basilisk is male because it has a red plume on its head.
 * Newt Scamander stated in Fantastic Beasts and Where to Find Them that there have been no recorded sightings of Basilisks in Britain for the last 400 years. Harry Potter wrote in his copy of the book "that's what you think".
 * Wearing glasses will not protect a person from the fatal effect of the basilisk's stare, because glasses still allow one's line of vision to connect directly and clearly with the serpent's eyes, unlike looking in a mirror or through a camera.
 * It has been theorized that spiders fear basilisks because arachnids can see 360-degrees around them and cannot shut their eyes, leaving them extremely vulnerable to the monster's killing gaze.
 * In the film adaptation of Harry Potter and the Chamber of Secrets, Harry watches the basilisk by its shadow on the floor.
 * Rubeus Hagrid asked Aragog "many times" to name this creature, but Aragog refused to speak of it.

Appearances

 * Harry Potter and the Philosopher's Stone (video game) 
 * 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
 * Fantastic Beasts and Where to Find Them
 * Harry Potter: A Pop-Up Book
 * LEGO Harry Potter: Building the Magical World
 * LEGO Harry Potter: Characters of the Magical World
 * LEGO Harry Potter: Years 1-4
 * Harry Potter LEGO Sets
 * Harry Potter and the Forbidden Journey
 * Pottermore
 * Harry Potter for Kinect