Enemies of the Heir, beware! is engraved on the wall when the Chamber of Secrets is first revealed. The fact that the Heir is meant to be the Slytherin Heir becomes widely known in some way.
The four Hogwarts Founders are mentioned by Professor Binns as he is lecturing Harry’s class on the legend surrounding the Chamber of Secrets: Godric Gryffindor, Salazar Slytherin, Rowena Ravenclaw, and Helga Hufflepuff. He says that Salazar Slytherin was the lone opponent of the other three when the Founders disagreed over whether to allow anyone who could not demonstrate magical ancestry. After the dispute, Slytherin allegedly departed the building carrying a monster-containing Chamber of Secrets. Nobody at Hogwarts has discovered even a single broom closet of secrets in the centuries that have passed, according to Binns.
Harry notices that Justin Finch-Fletchley is going to be bitten by a snake at the Dueling Club. Harry gives the snake the go-ahead to back off. As a result of the confusion, Ron and Hermione approach Harry and question him about this power. It seems that Salazar Slytherin and his successors are connected to the ability to speak to snakes, or being a Parselmouth. Given how little he is aware of his past, Harry questions if he may be Slytherin’s heir.
We observe a huge statue of a wizard within the Chamber, which Harry interprets to be Salazar Slytherin. We also get to know Tom Riddle, who turns out to be the Slytherin family’s heir. Despite being just in spirit, he has been in charge of Ginny and used her to assume the role of Slytherin’s heir. We also encounter a basilisk, the Monster of the Chamber.
Marvolo Gaunt exhibits two items that are intended to demonstrate his ancestry in support of his apparent notion that he is above a common lot of magic and, in turn, somewhat beyond the law. One item, a locket with a snake creating the letter S, is allegedly Salazar Slytherin’s. While Caractacus Burke claims, in Professor Dumbledore’s recollection, that the provenance of the locket was obvious to him, he subsequently sells it to him for a pittance.
We don’t learn much about Slytherin in this book except Voldemort’s attempts to recapture and destroy Slytherin’s locket, his declaration that he is the heir to the house, and his attempt to outlaw all other school houses save for Slytherin.