Creatures
Basilisk
The Basilisk of Salazar Slytherin is a giant serpent set in the Chamber of Secrets. Its stare kills, and a reflected or indirect look petrifies. Tom Riddle’s memory opens the Chamber in Harry’s second year. Harry kills the serpent with the Sword of Gryffindor, and a fang destroys the diary Horcrux.
In the books
Harry Potter and the Chamber of SecretsChapter: The Chamber of Secrets
Harry meets the serpent in the Chamber. Earlier in the same book, Hermione identifies it from a torn library page before she is petrified.