Hogwarts School of Witchcraft and Wizardry is the premier school in the Harry Potter series. The teachers at Hogwarts are entrusted with the magical education of students, so they can grow up to be the best witches and wizards in Britain. But, in the world of Harry Potter, not all professors are created equally.
While some teachers are excellent, others are mediocre, and some are downright evil. The worst of the worst use their positions of magical education to inflict pain on students or try to teach them to be evil as well. Hogwarts students definitely didn't want to learn from these professors.
7 Gilderoy Lockhart - Defense Against the Dark Arts
Gilderoy Lockhart is a master manipulator who takes advantage of a desperate situation to become the Defense Against the Dark Arts professor during Harry Potter and the Chamber of Secrets. He's written several books on his journeys trying to vanquish vampires, werewolves, hags, and ghouls. He winds up being the only applicant for the job when he gets it.
It's discovered that Lockhart is actually a mostly incompetent wizard who is only good at memory charms. He learns about the hard work of others, adjusts their memories, and takes credit for their adventures. Lockhart tries to wipe Harry's and Ron's memories only for the charm to backfire and wipe his memory while the three are in the Chamber of Secrets.
6 Severus Snape - Potions & Defense Against the Dark Arts
A bad man who does some good things, that's the best way to describe Severus Snape. He's a former Death Eater and servant of Lord Voldemort who turned spy for Dumbledore and the Order of the Phoenix. He swore to protect Harry Potter due to his infatuation, since childhood, with Harry's mother, Lily.
As a professor, he threatened to poison Neville Longbottom's toad and then punished the Gryffindor house when the toad was all right. He mocked Hermione Granger's buck teeth and constantly berated and belittled most of his students, especially Harry Potter. He was a sad and stunted man who had few redeeming qualities, but he still came through for Harry when Harry needed him most.
5 Quirinus Quirrell - Defense Against the Dark Arts
Noticing a trend? Very few of the Defense Against the Dark Arts teachers during the time the series takes place are good people. Quirrell represents the first plot twist of the series in Harry Potter and the Sorcerer's Stone. He is introduced as a pitiful and stuttering man who didn't really want to tackle the dark arts.
It's revealed that he is trying to steal the Sorcerer's Stone to bring back Lord Voldemort. He is evil and hiding it well. He is defeated by Harry Potter, and Lord Voldemort, who was living on the back of his head, left Quirrell to die.
4 Dolores Umbridge - Defense Against the Dark Arts
A government bureaucrat getting involved in education, what could go wrong? Dolores Umbridge was appointed as Defense Against the Dark Arts teacher by Minister of Magic Cornelius Fudge during Harry Potter and the Order of the Phoenix. She was sent to spy on Dumbledore because Fudge believed Dumbledore was trying to overthrow the Ministry by stoking fears that Voldemort had returned.
Umbridge refused to teach students practical lessons, insulted those she believed to be less than her, and punished anyone who challenged her, especially Harry Potter. After etching "I must not tell lies" into his hand with her bewitched quill, it was gratifying for many to hear him repeat it to her when she asked him to tell the centaurs "she meant no harm."
3 Amycus Carrow - Dark Arts
In Harry Potter and the Deathly Hallows, Lord Voldemort has essentially transformed the school into an evil educational center. One of his loyal Death Eaters, Amycus Carrow, is appointed as the Dark Arts teacher. There's no more Defense Against the Dark Arts.
Besides being a follower of the most evil wizard in history, he is also trying to teach other students to be evil. He crosses a line when he spits on Minerva McGonagall, leading Harry Potter to be able to angrily use the Cruciatus Curse for the first time.
2 Alecto Carrow - Muggle Studies
Much like her brother, Amycus, Alecto is a faithful servant of Lord Voldemort who is appointed to a teaching position once he has taken over the Ministry of Magic. Hogwarts needs a new Muggle Studies professor after Voldemort personally murders the previous one, and Alecto Carrow is more than happy to fill the void and revamp the curriculum.
She teaches students that Muggles are evil, and pureblood wizards are "rightfully" their superiors. Throughout history, those who have taught supremacy have been some of the most evil and that doesn't change in a fictional book series. She was also known to torture students who defied her.
1 Barty Crouch Jr. (Fake Mad-Eye Moody) - Defense Against the Dark Arts
Barty Crouch Jr. Is arguably the greatest of Lord Voldemort's Death Eaters. After breaking free of his father's Imperius Curse, Crouch reunited with Voldemort and worked with Peter Pettigrew to abduct Mad-Eye Moody as he was set to take over as Defense Against the Dark Arts teacher in Harry Potter and the Goblet of Fire.
He was actually an excellent professor, teaching the kids about the Unforgivable Curses. But he also set up Harry Potter for the journey to the graveyard that brought Lord Voldemort back to power. He could've been a great professor if he weren't evil.