As Dolores Umbridge was a sadist who enjoyed torturing students, Filch could relate to this. Also, as Umbridge granted Filch permission to torture misbehaving students, whereas Dumbledore would never even think of such things, he had loyalty to her. He is the only person who liked her at the school.
He apparently realised the Ministry of Magic was going to interfere at Hogwarts that school year, and clapped enthusiastically. Umbridge was a sadistic woman who, like Filch, enjoyed torturing and punishing students. Thus, the caretaker started to support Umbridge and follow her orders.
Filch hates all the students. Harry only attracts special treatment because he is unfortunate enough to draw Filch's attention on several occasions. Of course, in Chamber of Secrets, Filch thinks Harry has petrified Mrs. Norris, so he may hold an unreasonable and lingering grudge over the incident.
The confusion for audience members who have only watched the movies lies in Filch's dialect; although “ma'am” rhymes with “ham” in Standard American English, in some dialects of British English is rhymes with “farm.” Furthermore in some dialects of British English “r”s are deleted, so that pronouncing “ma'am” to sound ...
Umbridge and Filch Are RELATED - Harry Potter Theory
Why does Filch hate peeves?
To annoy Filch, Peeves trapped Mrs Norris in a suit of armour twice, dropped chandeliers and caused general mayhem, which Filch was later responsible for cleaning. For example, during the 1992-1993 school year Peeves dropped a heavy object on the floor above Filch's office after being goaded by Nearly Headless Nick.
Mrs Norris was the pet cat of Argus Filch, the caretaker of Hogwarts School of Witchcraft and Wizardry. Mrs Norris was described as having an unusually strong connection with her master, alerting him to any students misbehaving inside the school castle. She was described as appearing almost the same way as Filch.
Harry describes Umbridge to Sirius Black, saying that she's vile enough to be a Death Eater, despite not being one. Umbridge is also depicted to be a prejudiced person, despising half-breeds and Muggle-born witches and wizards to the point of firing Hagrid due to his half-giant birth status.
Harry was the most outspoken, which often landed him in trouble. She steadfastly stuck to the Ministry line that Voldemort had not returned and that Harry Potter's claims were only to get attention for himself.
Hagrid was a pupil at Hogwarts himself and was learning magic along with everyone else - until one horrible day in his third year, when he was expelled (for reasons we discover later on in the series). Although he was able to stay on as gamekeeper, his wand was snapped in half.
Mrs. Norris' looming presence in the Harry Potter series is far too magical for her to be an ordinary cat, and there's enough evidence to support a theory that she's a Maledictus like Nagini. Filch's nosy cat appears all throughout the book series and occasionally in the films.
Although Umbridge was not a Death Eater, and had no direct contact with Lord Voldemort, she showed that she was fairly in line with their goals. This was due to Umbridge's callous nature and her prejudiced beliefs, both of which were similar to Death Eater behavior.
Filch stops mid-sentence when he notices that the Kwikspell envelope is so close to Harry's elbow, and he asks hysterically whether Harry read it. Harry lied that he hadn't, and Filch seems quite alarmed and lets Harry go.
Why did he keep Filch around for so long? Dumbledore was a great wizard and a kind man who always valued gentleness over bitter resentment. Even with Filch's extensive knowledge of Hogwarts' secret passages and forbidden corridors, it makes no sense that Dumbledore would let someone punish his students so severely.
Apparently, Umbridge's mother was a Muggle and her brother was a Squib – a source of huge embarrassment for the family. Perhaps their abandonment and retreat back into the Muggle world had such a huge impact on Umbridge that it became the catalyst for her Muggleborn-targeted cruelty later on in life.
Bellatrix was an unapologetic monster who utterly relished in the pain and torment she caused, Umbridge was a monster but a monster in a pink coat, she could hide her evil behind a fake smile and supposed civility.
Was Umbridge a terrible person because of the Horcrux?
Despite this, some feel that her extreme cruelty in Deathly Hallows was given to the influence of Slytherin's Locket as a Horcrux, but J.K. Rowling has affirmed that this isn't the case and that the Locket couldn't worsen Umbridge as she was already such a horrible person.
This is what makes Umbridge's evil more sinister than Voldemort's; it is far more real, much like that which Kesey depicts through Nurse Ratched, who torments and dominates the patients in her care (and eventually sees one lobotomized).
If you have only seen the films, you might be surprised to hear that it wasn't Cho Chang who betrayed Dumbledore's Army to Professor Umbridge – it was Marietta Edgecombe. A friend of Cho's and a fellow Ravenclaw, Marietta (reluctantly) joined the DA.
When the centaurs made threatening moves, Umbridge cast "Incarcerous" on the centaur Magorian, strangling him with ropes. The centaur Bane then picked her up and carried her away deeper into the forest screaming (what happened to her beyond that, during her time with the Centaur herd until she was rescued, is unknown).
The Harry Potter movies seem to have started this idea, since in Harry Potter and the Deathly Hallows, Filch called McGonagall "ma'am," and some audiences thought he had said "mom." Of course, there has never been any indication that these two were related.
Argus Filch's evil tendencies were especially prominent when Dolores Umbridge was headmaster of Hogwarts, and Filch was more than keen to help her discipline students. In the end, Argus Filch never actually turned evil, but Harry Potter fans probably wouldn't have been surprised if he did.
Ginny wrote the messages with chicken (or rooster) blood. You would NOT know this from the movie! We have several hints from the book, though. Hagrid goes to see Dumbledore about putting an enchantment on the chicken coop.
