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. Basilisk breeding was banned in Medieval times.

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 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 immediately kill anything who looks into them. If the victim looks indirectly at the Basilisk's eyes, i.e. as a reflection or through an object, they will only be petrified. Ghosts may become petrified by the Basilisk's gaze as well, if they stare directly at it as was Nearly-Headless Nick. This is because ghosts are already dead, so they cannot die again. But Phoenixes (and possibly other non-human associated creatures) are immune to this deadly gaze. Spiders, such as Aragog, are terrified of the Basilisk, as they describe it as their enemies, and would not even speak of it.

The Basilisk's sharp fangs are full of deadly venom, powerful enough to kill a human in a matter of minutes. The venom is potent even long after death. It is also one of the few substances destructive enough to destroy a Horcrux, as Phoenix tears are the only known cure. Basilisk skin is armored 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. 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.

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 fang was removed from the snake's body. The venom is one of the few known substances that can 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.

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, due to them both being born in a chicken's egg under a toad or serpent, but usually the creatures are born from the opposit way, the basilisk can be hatched by a rooster from the egg of a serpent or toad and the cockatrice by the reverse way, which is hatched from a rooster's "egg" incubated by a serpent or toad, able to petrify their victims through eye contact, and would die if they hear the crowing of a rooster.
 * 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.

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
 * Fantastic Beasts and Where to Find Them
 * Lego Harry Potter: Years 1-4

Notes and references
Basilic Василиск Basiliski