This jinx was cast by Tom Marvolo Riddle, who was by the time known exclusively as Lord Voldemort, to curse the Hogwarts school's Defence Against the Dark Arts class to ensure that none of its applicants could hold their post for more than one year. It is unknown what the requirements and incantation of this jinx are, or if it could be used for other school subjects or other establishments and careers. The jinx will be lifted once the caster is dead.
Upon his graduation from Hogwarts, Tom Riddle asked the then Headmaster, Armando Dippet, for the post as Professor for the Defence Against the Dark Arts class, due to his love for Hogwarts and passion for the Dark Arts. Professor Dippet rejected Riddle's application, because he was too young at eighteen years old, but offered him to reapply after a few years.
Over a decade later, when Riddle resurfaced as the mysterious Lord Voldemort, he returned to Hogwarts to ask for the job once again. At this time, Albus Dumbledore had taken over as Headmaster and, knowing of Voldemort's harmful intentions, rejected his application. Although Voldemort was merely using the application as an excuse to return to Hogwarts to do research into dark magic, recruit more followers and to hide his diadem Horcrux, he was still infuriated that his return to the school had been denied. In revenge, Voldemort jinxed the position to ensure that no applicant of the Defence Against the Dark Arts post could keep it for more than one year.
- "You have had five teachers in this subject so far, I believe. Naturally, these teachers will all have had their own methods and priorities. Given this confusion I am surprised so many of you scraped an O.W.L. in this subject. I shall be even more surprised if all of you manage to keep up with N.E.W.T. work, which will be much more advanced."
- —Professor Snape on the curriculum's instability due to the jinx's effect.[src]
A secondary and more strategic reason for jinxing the post could be Voldemort's wish to reduce the quality of the teaching of the subject, as its purpose was directly opposed to his personal goals. Disrupting the teaching by an annual change of staff would make future students less capable of self-defence.
Known victims of the jinxEdit
Once Voldemort placed his jinx on the post, around the end of each school year, the teachers of the class are forced to leave due to one reason or another, from the effects of the jinx.
- Quirinus Quirrell: 1991–1992 school year, died when he suffered excruciating pain from Harry Potter's love-protection and when Voldemort's fragmented soul left his body.
- Gilderoy Lockhart: 1992–1993 school year, lost his memory due to a backfiring Memory Charm with a broken wand, sent to St Mungo's Hospital for recuperation, never fully recovered.
- Remus Lupin: 1993–1994 school year, revealed by rival teacher Severus Snape to be a werewolf, forced to resign due to parents' protests and safety of the school.
- Barty Crouch Jr: 1994–1995 school year, Alastor Moody claimed to be only teaching a year before retiring: turned out to be Barty Crouch Jr in disguise, Barty received the Dementor's Kiss, Moody was imprisoned in his own magical trunk for almost one year and did not teach at all, hinting that the fact he was appointed made him a victim too.
- Dolores Umbridge: 1995–1996 school year, removed when Cornelius Fudge was forced to accept that Voldemort had indeed returned, leading to the abolishing of all of Umbridge's Educational Decrees.
- Severus Snape: 1996–1997 school year, escaped when he murdered Albus Dumbledore, which was secretly planned with the Headmaster to spare him the pain of a curse, abandoning the post in the process.
- Amycus Carrow: 1997–1998 school year, arrested after Voldemort's demise for membership in the Death Eaters organisation.
The jinx liftedEdit
After Voldemort's downfall, the jinx was broken and Hogwarts was able to keep a permanent Defence Against the Dark Arts teacher. At the very earliest it would have been lifted once he gained control of the Ministry of Magic and Hogwarts.
Behind the ScenesEdit
In the films, several of these teachers suffer a slightly different fate. Quirinus Quirrell, instead of being burnt raw and red by Lily's protection, was burned completely to ash upon being in contact with Harry and crumbled to death. Barty Crouch Jr was not noted to receive the Dementor's Kiss, but he certainly fell into the custody of the authorities. Dolores Umbridge was suspended for suspicions on her activities in school, with an impending investigation (but then apparently removed later).
It is uncertain if Amycus Carrow ever would have been affected by this jinx, since the subject was replaced with the Dark Arts, treated as a new subject. However, it's also possible the magic could change its nature to jinx any teacher working with either of those branches of magic. However since Voldemort was effectively in control of Hogwarts during the 1997-1998 school year and intended to remain so, it would have been a hindrance to his goals to still have the jinx in place.
Tom Riddle put the jinx on the post to ensure no one would keep the place of D.A.D.A teacher. Coincidentally, three of his followers suffered the jinx which prevented him from getting his plans into action.
The concept of having the Defence Against the Dark Arts teacher suffer a horrible fate every year was inspired by the semi-fictional metal band Spinal Tap, which has a quantity of fictional past drummers who all died in various ridiculous ways. Incidentally, one of the drummers died by being eaten by their pet python, mirroring Snape's eventual fate of being killed by Nagini.
When Severus Snape was announced to be the next Defence Against the Dark Arts teacher during 1996, Harry Potter made a rather spiteful remark that he is glad that "Snape will be gone by the end of the year" and "keeping [his] fingers crossed for another death", after Quirrell died on the job four years back due to this jinx. Ironically, Harry got his wish when Snape killed Dumbledore (i.e. "another death") and abandoned his post.
The jinx was presumably implemented in the 1970's, meaning approximately 25-27 witches/wizards were subjected to its effects before Voldemort's death.