Jinx on the post of Defence Against the Dark Arts teacher

"You see, we have not been able to keep a Defence Against the Dark Arts professor for more than a year since I refused the post to Lord Voldemort."

- Albus Dumbledore

This curse was employed by Tom Riddle, who was at the time known as Lord Voldemort to curse the Hogwarts school's subject Defence Against the Dark Arts to ensure that none of its applicants can hold their post for more than one year.

Usage
Upon his graduation from Hogwarts, Tom Riddle asked the then Headmaster, Armando Dippet, for the post as Professor of 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 returned as Lord Voldemort, he returned to Hogwarts to ask for the job once again. By this time, Albus Dumbledore has taken over as Headmaster, and knowing of Voldemort's ill-intentions, rejected his application. Although Voldemort was merely using the application as an excuse to return to Hogwarts to do his own dark researches, recruit more followers, and to hide his diadem Horcrux, he was still infuriated to be denied his chance to return to school. In revenge, Voldemort employed this curse to ensure that no applicant of the Defence Against the Dark Arts post can keep their position for more than one year.

Known Victims of the curse
Once Voldemort placed his curse 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 curse.
 * Quirinus Quirrell: 1991–1992 school year, died when he suffered excruciating pain from Harry Potter's love-protection, as well as 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.
 * 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.
 * Alastor Moody: 1994–1995 school year, 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 did not teach at all.
 * Dolores Umbridge: 1995–1996 school year, removed when Cornelius Fudge was forced to accept the return of the Dark Lord, leading to the abolishing of Education Decree Numbers 22 to 28.
 * 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 organization.

The curse lifted
After Voldemort's downfall, the curse is lifted and Hogwarts was able get a permanent Defence Against the Dark Arts teacher.

Behind the scenes

 * It is possible that Voldemort lifted the curse himself at the start of the 1997–1998 school year in favour of his servant, Amycus, so he may teach without being hindered by the curse.
 * Interestingly, those who are merely forced to leave the post rather than suffer severely during their respective year, they suffer later.
 * Remus Lupin was killed by Antonin Dolohov four years later at the Battle of Hogwarts,.
 * Alastor Moody, although not have officially taught the class, was killed by Voldemort two years later during Battle over Little Whinging.
 * Dolores Umbridge was sent to Azkaban two years later for her crimes against Muggle-borns.
 * Severus Snape was killed by Nagini under Voldemort's command, for the mistake of the ownership of the Elder Wand.