Who is Umbridge?
Dolores Jane Umbridge was one of Harry Potter's interrogators as he is tried on charges of unauthorised practice of underage sorcery before the Wizengamot, a wizard's court. She is Senior Undersecretary to the Minister of Magic, Cornelius Fudge, and is described as looking like a large pale toad, wearing a little black velvet bow in her hair that reminds Harry of a fly about to be caught.
Umbridge was posted to Hogwarts School of Witchcraft and Wizardry as the new Defense against the Dark Arts teacher by order of the Ministry, teaching according to a politically restricted curriculum which would result in the students learning strictly the theory of Defence Against the Dark Arts; without the teaching of practical applications, most of the students feel that they will be left defenceless against the Dark Arts.
Her power increases when she is appointed High Inquisitor of Hogwarts in which position she proceeds to evaluate the teachers at Hogwarts. With her new power, she fires Sybil Trelawney, professor of Divination, and is offended when Dumbledore replaces Sybil with a centaur, since as a mixture of human and horse he is regarded as a "filthy half-breed".
With the formation of an Inquisitorial Squad, which rewards some students for reporting on others and sanctions them to act as enforcement goon squads. She tries to prosecute Harry for forming the Defence of Dark Arts club, DA, but Dumbledore takes the blame, and leaves Hogwarts. Umbridge replaces him as Headmaster. She fires Hagrid, another mixed-race teacher as well, and injures Professor Minerva McGonagall while doing so.
She interferes with Harry's attempt to contact his godfather Sirius Black, but is outwitted by Hermione Granger, who tricks her into going into the Forbidden Forest, where she is subdued and almost killed by a herd of centaurs.
After Voldemort had finally revealed himself from the wizarding world and was chased away by Dumbledore, Umbridge is removed from her position as Headmistress, and is driven from the school by Peeves the Poltergeist.
Why we hate her so much...
▫ She interrupts Dumbledore during his announcements and then proceeded to bore the school half to death with her speech.
▫ She annoys us with 'hem hem'.
▫ She makes Harry write 'I must not tell lies' with a quill that cuts into skin and writes with his blood.
▫ She has the most boring DADA lessons ever.
▫ She gave Harry a lifetime ban from Quidditch.
▫ She looks weird.
▫ She deliberately ignores Hermione when she has her hand up.
▫ She deliberately provokes Harry.
▫ She hands out stupid Decrees.
▫ She blocked out Floo throughout the whole school except for her office.
▫ She confiscated Harry's beloved Firebolt! What could be worse?
▫ And many more...