Elaborate, if necessary: In a nutshell, Dolores Umbridge is a nasty piece of work. It’s unclear exactly how old she is by the time Order of the Phoenix rolls around, but she’s not young anymore for sure, and has assumedly been in the Ministry of Magic for quite some time, having leaped up the ranks at a relatively young age. She’s not a particularly gifted witch; in fact, it would be well within the bounds of reason to assume that she’s not very prominent at all as far as casting spells goes (perhaps because of her intense rigidity), especially when looking at her wand, which is described as being “unusually short.” Instead of leaning on being a talented witch, she had to rely on being very knowledgeable and prominent in the political sense in order to get herself up to the post she currently enjoys full reign of: Senior Undersecretary to the Minister for Magic himself. And she’s not above boasting about it, either. In actuality, a lot of what Umbridge is and does is simply a bunch of hot air, meaning she talks a lot. She knows how to suck up to the right people, simpering to them so that they might favour her; yet another reason why she climbed the ranks of the Ministry so fast. She now considers herself close to Cornelius Fudge and is his most trusted member of staff, a feeling which only strengthened when he sent her to take the post of Defence Against the Dark Arts professor at Hogwarts in order to spy on Dumbledore and keep the students from forming some sort of organization against the Ministry under Dumbledore’s leadership.
However, the truth behind Dolores Umbridge is something much more sinister. While she appears for all intents and purposes within the Ministry to be looking out for the well-being of those around her, especially the students whom she is currently teaching, the truth could not be more different. Ultimately, Dolores is only out for her own well-being and she will literally do anything to keep her post and reach her goals, whatever they may be. She may not be a very gifted witch in the magical sense, but she has been known to use torture for information or whatever result she desires and is knowledgeable about the Unforgivable Curses. Later in Order of the Phoenix, past the point she is taken from here, she nearly uses one (the Cruciatus Curse) on Harry when he refuses to tell her who he was trying to contact in her fireplace, and the only reason she doesn’t is because Hermione finally cracks and tells her.
The biggest part of her personality is her utter lack of conventional morals. She will do anything to gain power, keep it, lord it over others, and take absolute and utter control. She loves having power. Climbing the ranks of the Ministry so quickly proved this. She loves keeping it and isn’t above backstabbing people or making deals to secure her position (or perhaps information, as she did with Willy Widdershins and the regurgitating toilets). She’s also known to take bribes from people, as she does later in the series, agreeing to take a locket necklace off Mundungus Fletcher’s hands in exchange for not fining him for breaking a rule of magical trading. Dolores is very secure in her position as Senior Undersecretary to the Minister and uses it to influence Cornelius quite often. She has also been known to take matters into her own hands when things aren’t quite going the way she wants them to. The position of High Inquisitor at Hogwarts was created solely for her so that she could oversee everything that went on at the school and every time someone tried to make some sort of disagreement with her or rose above her in power, she sought a way, no matter what she had to do, to strip them of that power. Most of the Educational Decrees handed down in that one single year were because she twisted Cornelius’ arm. Dolores has also been known to take what some would call ‘cowardly’ or ‘backstabbing’ ways, as happens when she takes a group of Aurors down to attempt to arrest Hagrid during the middle of the night. Most unfortunately, they fail, though not for lack of trying. However, amongst the insanity, Dolores and her companions Stunned Minerva McGonagall - in the middle of the night and completely without warning.
“What Cornelius doesn’t know won’t hurt him.” To a true Slytherin, and there can be no doubt that Madam Umbridge is one, the end ALWAYS justifies the means. Always. This blatant disregard for the safety and comfort of those around her makes her a formidable opponent and dangerous ally.
Professor Umbridge also hates, loathes, despises even, half-breeds of any kind. They make her utterly ill and if it’s a choice between hell and the company of a part-human, she’d take hell, no questions asked. That being said, she’s known to be absolutely vicious towards part-humans, having drafted a bit of anti-werewolf legislation herself so that the law makes it nearly impossible for werewolves, such as Remus Lupin, to secure jobs. She doesn’t care how many people she upsets or how many lives she destroys in her quest for power. As long as she has that power and as long as she can keep it, she’ll be happy. Of course, whether a happy Dolores or an upset one would be best for society is anyone’s guess at this point.
Power corrupts, indeed.
Relationships: (to name only a few)
Harry Potter: She thinks he’s a nasty little boy and a liar to boot. It was she who sent the dementors after him over the summer, something she feels no remorse for, and the fact that he weaseled out of punishment irritated her beyond belief. Another part of the reason she took the post of Defence Against the Dark Arts Professor at Hogwarts was to discredit both Harry and Dumbledore. For his detentions especially, she enjoys using one of her special quills, which literally carves the words he’s writing onto the back of his hand and uses the blood for ink. His constant toeing the line and outbursts do little to annoy her; in fact, she seems to take pleasure in goading him so that she can punish him. After all, she’s not the one who’s a bad little boy.
Albus Dumbledore: Oh she would love to get him sacked and she’s definitely trying her hardest. He’s a little off his rocker as far as she’s concerned and a danger to a healthy pure-blood society… one that is not in danger from You-Know-Who, thank you very much.
Minerva McGonagall: Simply put, they loathe each other. Dolores believes Minerva holds too much power in the school, more than Dolores herself has, and that must change. Dolores is above nothing to get her to leave… as proven the night she and her Aurors nearly kill Minerva and damn if Dolores in the future wishes they had.