"Of the many fearsome beasts and monsters that roam our land, there is none madami curious or madami 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 aklatan book.[src]
The Basilisk is a giant serpent, also known as the King of Serpents. It is a creature bred sa pamamagitan ng Dark Wizards. Herpo the Foul was the first to breed a Basilisk; he accomplished this sa pamamagitan ng 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 sa pamamagitan ng 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.
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 sa pamamagitan ng seeing it through another object.
Phoenixes are immune to this deadly gaze, and 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 sa pamamagitan ng 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 sa pamamagitan ng a single scarlet plume on its head.