A basilisk lives in the Chamber of Secrets beneath Hogwarts in Harry Potter and the Chamber of Secrets.
The creature was placed there by Salazar Slytherin, one of Hogwarts’ founders. Slytherin created the hidden chamber and left behind a monster that could be controlled by his heir. Tom Riddle, the teenage form of Lord Voldemort, later opened it through his connection to Parseltongue.
The basilisk’s direct gaze is deadly, while seeing it indirectly can produce different effects. Harry survives because he sees only a reflection in a ghost’s camera, and later through Nearly Headless Nick’s ghostly form. Hermione and Penelope Clearwater are petrified after viewing a reflection.
The basilisk is ultimately killed by Harry with the Sword of Gryffindor. Harry then uses one of its venomous fangs to destroy Tom Riddle’s diary, which is a Horcrux.