Dolores Umbridge seemed to hate Harry from the beginning. Why? I don't think Harry met Umbridge before Order of the Phoenix, yet she sent Dementors after him, said Harry had to be taken care of, etc. I don't recall her explaining why she hated Harry.
Note: this question was inspired by the question at http://www.cosforums.com/archive/index.php/t-104601.html
Umbridge's story on Pottermore posted in November 2014 makes clear 3 reasons for her persecution of Harry Potter:
She welded herself to Cornelius Fudge politically, and (as we know from the books) Fudge's Party Line was that Dumbledore was aiming to unseat him as MoM, and Harry was a lying kid serving that end with his lies about "He Who Must Not Be Admitted To Have Returned".
In essence, discrediting Harry would be a big win for her patron Fudge, and vice versa.
As the Minister for Magic Cornelius Fudge became increasingly anxious and paranoid that Albus Dumbledore had ambitions to supersede him, Dolores managed to claw her way to the very heart of power, by stoking both Fudge’s vanity and his fears, and presenting herself as one of the few he could trust.
Umbridge hated muggles and muggleborns.
As such, Harry was a bad thing both as a half-blood, AND as a symbol to those who held pro-Muggle and anti-bigoted views.
After a glass of sweet sherry, Dolores was always prone to spout very uncharitable views, and even those who were anti-Muggle found themselves shocked by some of Dolores’s suggestions, behind closed doors, of the treatment that the non-magical community deserved
Umbridge was a control freak, who saw Harry as a challenge to her authority, and her response to such a challenge was to stamp that out:
Dolores’s appointment as Inquisitor at Hogwarts gave full scope, for the first time in her life, for her prejudices and her cruelty. She had not enjoyed her time at school, where she had been overlooked for all positions of responsibility, and she relished the chance to return and wield power over those who had not (as she saw it) given her her due.
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Dolores has what amounts to a phobia of beings that are not quite, or wholly, human. Her distaste for the half-giant Hagrid, and her terror of centaurs, reveal a terror of the unknown and the wild. She is an immensely controlling person, and all who challenge her authority and world-view must, in her opinion, be punished....
She didn't personally hate him. She was just trying to do her job and quite honestly she was a bit mean.
Umbridge was also a cool-demeanoured sadist who rarely expressed the extent of her anger openly, casually making decrees and handing out torturous punishments with a smile (most notably, forcing Harry to carve "I will not tell lies" into the back of his hand with a Blood Quill). She created several new rules and regulations in order to increase control and chances to punish students, despite many of them being ridiculous and unfair.
The Ministry sent her to do a specific job if she hadn't of completed it she would have been in trouble and would have lost some of her power. From the following quote we can see she wouldn't of liked that. She exerted her power to the full extent, I mean she did almost kill Professor McGonagall.
She was depicted using any means to maintain her personal power and the political power of her bosses. She committed attempted soul-removal (via the Dementor attack on Harry), solicited bribes, and tortured children to achieve her goals.
And she even hated her own family.
Her younger brother was a Squib but she herself was born a witch. Under her father's influence, she despised her Muggle mother and her Squib brother, considering them inferior to her and her father, and they both denounced them.
It really wasn't just Harry she hated everyone who didn't have power to stop her. It was because she felt bad about herself.
Following Voldemort's takeover of the Ministry of Magic in 1997, Umbridge resumed her post as Under-Secretary and oversaw the registration and persecution of Muggle-born witches and wizards. She conducted trials with sadistic pleasure, subjecting innocent Muggle-borns to the presence of Dementors and sending them to Azkaban for supposedly stealing magic from "real" witches and wizards
Cos Forums has some interesting takes on it.
From User Fellyphone:
I think the original reason why Umbridge had a beef against Harry had to do with her wanting power and she saw Harry as a threat because he associated himself with Dumbledore. Rather than get rid of Dumbledore right away, she sought to discredit Harry and to wreck havoc on his summer by sending out the dementors.
Harry would never shut up about what happened and that undermined her authority since she was suppose to "stop lies" and do the Ministry's bidding.
From User Saiorri:
I think like a lot of other people, especially the ones who wanted to discredit Dumbledore, Umbridge wanted to silence Harry just to prove he's human and not "The Chosen One." Umbridge didn't have to know Harry to discredit him. He was trying to tell everyone that LV was back, when the Ministry was saying LV was a done deal from over a decade ago. I was just talking to my mother about this the other day. Imagine, if you will, that we didn't know that Hitler shot himself instead of being defeated by his last victim, and we didn't have a body to prove he was gone, and then some kid claims "Hitler" did some murders in Israel in 1958 and he was there-----if you lived in Israel, would you want to believe he was back?!?! ......
We need to remember, she had Voldemort's necklace around her neck... remember what it did to Ron, Harry when wearing it? When Harry went into the pool to fetch the sword, it tried to kill him... so it should stand to reason that it could have had a strange effect on the Dolores not only wanting to silence Harry, but maybe to even kill him to along with Dudley.
