Hogwarts was founded around 990 A.D. by four of the greatest wizards and witches of the age: Godric Gryffindor, Helga Hufflepuff, Rowena Ravenclaw, and Salazar Slytherin. They each represented an aspect of personality that they wanted to bring out in new students. However, shortly after founding the school, Slytherin had a falling out with the other founders about blood purity, and wanted to admit only pure-blood students. He felt pure-blooded students deserved to learn magic, and those of other ancestry such as Muggle-borns and Half-bloods, were unworthy. The other three founders all disagreed, especially Gryffindor. Slytherin left the school, but not before secretly building the Chamber of Secrets. He foretold that only his own heir would be able to open it once they arrived at the school, and the heir would unleash a murderous basilisk living inside to purge the school of all Muggle-born students.

During the 1700s, there was a proposal to install an elaborate plumbing system in the castle. This threatened the secrecy of the Chamber of Secrets, forcing Corvinus Gaunt, a Slytherin student, descendant of Salazar Slytherin and Parselmouth, to protect the entrance to the Chamber by having it concealed behind plumbing fixtures and sinks in second floor girls' bathroom, so only future heirs of Slytherin would know how to open the Chamber.



Many Centuries later, Tom Marvolo Riddle (Lord Voldemort) , opened the Chamber in his fifth year. When a girl named Myrtle Warren was killed, the Ministry of Magic threatened to close the school. As Riddle spent his time away from Hogwarts in a Muggle orphanage, he did not want the school closed. His request to remain in school over the holidays was denied due to the situation he created. Upset with himself, he framed Rubeus Hagrid, and although Albus Dumbledore still suspected Riddle, Hagrid was expelled, and Riddle got off without punishment. However, in 1992, the Chamber was reopened, and it was discovered that Hagrid was innocent and Riddle was guilty.