A Basilisk is also known as the King of Serpents. It is a snake that may reach gigantic size and live for hundreds of years. A basilisk is born from a chicken's egg, hatched beneath a toad. The basilisk has the ability to kill anyone who looks at it directly in the eye. If a person sees the basilisk indirectly he or she can still be Petrified. Basilisks also have deadly and venomous fangs. Basilisk venom is one of the few things that can destroy a horcrux. Spiders flee from a basilisk, as it is their mortal enemy. The crowing of a rooster is fatal to a basilisk. 
 The Basilisk in Harry Potter and the Chamber of Secrets
In Harry Potter and the Chamber of Secrets it is revealed that a Basilisk is the monster which lives in the Chamber of Secrets. This Basilisk can only be controlled by the Heir of Slytherin, by means of Parseltongue, and even if another person is capable of speaking Parseltongue, they cannot control the Basilisk. When Harry Potter goes into the Chamber of Secrets and meets Tom Riddle (the memory of him from his diary horcrux), Riddle unleashes the Basilisk on Harry, who must fight it. Along with the help of Fawkes, who pecks out the eyes of the Basilisk so that nobody can die from looking at its eyes any longer, Harry stabs the Basilisk with the Sword of Gryffindor, embedding Basilisk venom, an extremely destructive substance into the Sword.