The Heir of Slytherin was a descendant of Salazar Slytherin who spoke Parseltongue and were able to open the Chamber of Secrets and control the Serpent of Slytherin. There were several Heirs through the centuries since Slytherin left the school but Tom Riddle was the descendent who let the Serpent loose in the school to fulfil the purpose of the Heir of Slytherin but he was unsuccessful.
In the 10th century, having failed to persuade the co-founders of Hogwarts School to ban Muggle-borns, Salazar Slytherin created the Chamber of Secrets prior to abandoning the school and put in it the Serpent of Slytherin in the hope it would eventually purge the school of Muggle-born students.
He ensured that the Serpent could be controlled only by Slytherin and any heirs who would inherit the skill of speaking Parseltongue. Knowledge of the Chamber's existence was passed through each generation of descendants and several opened the Chamber in that time but it was a thousand years until an Heir let the Serpent of Slytherin loose in the school. Even though Parseltongue was the skill needed to open the Chamber, it could be opened by anyone who spoke it even if they were not an Heir of Slytherin, but the Serpent of Slytherin could not be controlled by anyone else.
1942 - 1943 school year
In the 1942-1943 school year, an Heir of Slytherin finally opened the Chamber to complete Slytherin's "noble work". Tom Riddle was a descendent of Salazar through the Gaunt family. But eventually a student was killed when she heard Tom speaking to the Basilisk near the entrance to the Chamber, and she looked into the Basilisk's eyes. The school was going to be closed down, but Tom knew he would have to go back to the Muggle orphanage where he was raised. He closed down the Chamber of Secrets, having framed a Rubeus Hagrid and Aragog for what happened.
Before he graduated, Tom enchanted a Diary to be a Horcrux. It was capable of possessing a reader to open the Chamber of Secrets again, communicating whatever it wants to a future reader, and a version of Tom at the age of 16 was preserved and could siphon a possessed's life force to gain a physical body of its own.
1992 - 1993 school year
In the 1992-1993 school year, Tom Riddle's Diary possessed Ginevra Weasley and she opened the Chamber for the second time. She gave the school a warning on the wall of a corridor in paint: "THE CHAMBER OF SECRETS HAS BEEN OPENED. ENEMIES OF THE HEIR BEWARE". The whole school thought for a long time that Harry Potter was the Heir of Slytherin. He suspected it was Draco but that was proven wrong, and the Diary told Harry it was Hagrid but he spoke to Aragog and saw it was a lie. Harry later found the Chamber of Secrets and destroyed the Basilisk and Diary.
Known Heirs of Slytherin
Notes and sources
- Harry Potter and the Chamber of Secrets, Chapter 9
- Harry Potter and the Chamber of Secrets, Chapter 13
- Harry Potter and the Chamber of Secrets, Chapter 17
- Harry Potter and the Chamber of Secrets, Chapter 16
- Harry Potter and the Chamber of Secrets, Chapter 8
- Harry Potter and the Chamber of Secrets, Chapter 12
- Harry Potter and the Chamber of Secrets, Chapter 15