Manic Pixie Nightmare Girl
We never imagined that the adjectives "cute," "perky," "sunny," and "smiley" could ever make our blood run cold with fear. But that was before we met Dolores Umbridge.
The first time we see Dolores Umbridge, she's sitting on the Wizengamot and she doesn't think much of the idea that dementors would have attacked a bunch of Muggles. This Harry Potter kid must be a liar. Let's throw him out of Hogwarts, right?
And yeah; that's not great. But, when she shows up as the Defense Against the Dark Arts teacher at Hogwarts, things get seriously bad:
DOLORES UMBRIDGE: You will be learning about defensive spells in a secure, risk-free way.
HARRY POTTER: Well, what use is that? If we're gonna be attacked it won't be risk-free.
DOLORES UMBRIDGE: Students will raise their hands when they speak in my class. It is the view of the Ministry that a theoretical knowledge will be sufficient to get you through your examinations, which after all, is what school is all about.
HARRY POTTER: And how is theory supposed to prepare us for what's out there?
DOLORES UMBRIDGE: There is nothing out there, dear! Who do you imagine would want to attack children like yourself?
HARRY POTTER: I don't know, maybe, Lord Voldemort!
That's right. Umbridge is at Hogwarts to peddle the Ministry line on Voldemort. She's totally in Fudge's corner and she will not tolerate any dissent. Students will raise their hands. Voldemort is not back. And absolutely no going to the bathroom without a hall pass.
But Umbridge isn't just hanging around Hogwarts to suck up to the Minister of Magic. She's also in it for her own personal gain. Deep down inside, she's power-hungry and ambitious and she'll stop at nothing to get what she wants. She's got no problem torturing children during detention. Or questioning students with truth potions. Or even using illegal curses if it means she gets the information she needs.
It's like Hermione says—she really is a "foul, evil, old gargoyle."
Even compared to the other Defense Against the Dark Arts teachers Harry's had to deal with, Umbridge really takes the cake. Lockhart liked to brag. Lupin was a werewolf. Moody was a Death Eater in disguise. Quirrell turned out to be helping Voldemort. But, none of them tortured students in their spare time and used their government connections to take control of the school.
Maybe Voldemort needs to start recruiting women who collect kitten plates?
In the end, Umbridge is so certain of her own power and authority at Hogwarts that she isn't careful when she's walking around in the Forbidden Forest. She insults and group of centaurs and gets hauled off into the night.
Good riddance to very, very bad teachers.