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.