During Harry's time at Hogwarts, he certainly had more than his fair share of Defense Against the Dark Arts teachers. So many people held the position that it was rumored it had been cursed by Voldemort when he was denied the job by Dumbledore.
With so many teachers filling the role, the quality and personality of its holders were mixed. Some were truly inspiring teachers, like the well-liked Remus Lupin, who continued to teach despite suffering from Lycanthropy, while Dolores Umbridge, the sadistic pink-clad teacher, and Ministry official, was his complete opposite.
Gilderoy Lockhart
Before teaching at Hogwarts, Gilderoy Lockhart was already a well-known and established figure. He'd written a pile of books about his experience fighting evil wizards and dangerous creatures, and he seemed to be a highly-skilled, if egotistical individual.
During his time as DADA teacher, it became clear that he wasn't quite the brilliant wizard he claimed to be. When the Chamber of Secrets is opened, he tries to flee rather than face the Basilisk, and gets a chance to show off his proficiency in one type of spell, the Memory Charm, which backfires on him, rendering him insensible.
Amycus Carrow
Following the death of Dumbledore and the collapse of the Ministry, Snape is appointed headmaster of Hogwarts and sets about harsh governance. Helping him are two of Voldemort's top Death Eaters, Amycus and Alecto Carrow. While his sister becomes a professor of Muggle Studies, Amycus takes on the role of Defense Against the Dark Arts teacher.
Amycus is one of the worst teachers to ever serve at Hogwarts. His subject has been changed from Defense Against the Dark Arts to simply The Dark Arts, and includes teaching the unforgivable curses. Aside from his teaching, Amycus and his sister are also in charge of discipline, which includes torturing students with the Cruciatus curse.
Quirinus Quirrell
On his first appearance, Quirrell didn't seem to be much of a Defense Against the Dark Arts teacher. He was a nervous and easily scared professor who used to teach Muggle Studies. Prior to taking up his new position, he had been traveling the world and had picked up his nervous nature and stutter during that time.
Unknown to anyone else, however, Quirrell had actually been taken over by Lord Voldemort, who had affixed himself onto the back of Quirrell's head, being disguised by the professor's large turban. He was destroyed during his confrontation with Harry over the Philosophers' Stone, becoming one of the series' most tragic characters.
Dolores Umbridge
Following Voldemort's return, Cornelius Fudge does everything he can to avoid facing up to the truth and installs Umbridge as Defense Against the Dark Arts teacher to look over the school and prevent Harry Potter from spreading the truth about the Dark Lord.
Umbridge is a sadistic teacher, delighting in torturing her students during detention, but she hides it all behind a curtain of bright pink outfits and pictures of kittens. Although she doesn't appear to be particularly skilled in magic, she is still powerful due to the amount of authority given to her by the Ministry of Magic and holds Hogwarts under her increasingly harsh rule.
Remus Lupin
Despite all the poor-quality DADA teachers Harry had to endure, if there was one who made up for it, it was Remus Lupin. Arriving at the school during Harry's third year, he quickly became one of the most popular teachers, with his enjoyable teaching style and genuine magical abilities.
Lupin suffered from Lycanthropy, a condition that caused him to transform into a werewolf every month during the full moon. When the news of his condition was revealed, terrified parents demanded that he be removed from his position as he was far too dangerous to be allowed in the school.
Severus Snape
Snape's impact on the Wizarding World is too big to be ignored. During the First Wizarding War, he turned against Voldemort and acted as a spy for Dumbledore. After Voldemort's defeat, he was given the position of potions master at Hogwarts, though he desired the post of DADA teacher instead.
During Harry's sixth year, he finally got the job he wanted, as Horace Slughorn replaced him as potions master. Snape was never a popular teacher, and most students outside Slytherin openly despised him. He was, however, an extremely powerful wizard, and his history as a former Death Eater surely made him one of the best people to advise about the Dark Arts.
Mad Eye Moody/Barty Crouch Jr.
Despite being a top choice for the role, Alastor Moody never got to serve as a professor at Hogwarts. Prior to taking up his position, he was attacked and held prisoner by Barty Crouch Jr. who used Polyjuice potion to pose as the former Auror.
Despite being an imposter, Barty Crouch Jr. played his part well, managing to fool all the Hogwarts staff into believing he really was Moody, and became a popular, if slightly terrifying teacher to many of the students. He also gained Harry's trust, guiding him through the Triwizard tasks and fulfilling the orders of his master Voldemort.
Albus Dumbledore
Dumbledore is one of the most powerful wizards to ever live. His exploits and achievements earned him fame across the Wizarding World and made him a top choice to be Minister for Magic, but Dumbledore choose to spend most of his life at Hogwarts, devoting himself to teaching future generations.
Although he's best known as the headmaster of Hogwarts, his career at the school actually began much earlier, when he taught Defense Against the Dark Arts, and later Transfiguration. As he would be heavily involved in the defeat of two powerful dark wizards, Dumbledore was one of the most qualified individuals to hold the position of DADA professor.