“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.”
—Excerpt from Most Macabre Monstrosities.
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.