A Professor at Hogwarts School of Witchcraft and Wizardry, Snape is hostile to Harry due to his resemblance to his father James Potter, who bullied Snape during their time together at Hogwarts. As the series progresses, Snape's character becomes more layered and enigmatic.
While through most of the series Snape seems to be horrible to Harry and possibly trying to get him into Voldemort's hands, it's revealed at the end of the series that Snape was actually helping watch out for Harry.
He lost a little respect for him the day he say him bullying Snape in his memories. From that day onwards he felt a pang of guilt everytime he felt proud of being James Potter's son.
He could just be angry that Harry found out about this incident, but that doesn't quite fit because he has told Harry on other occasions that his father was a bully. Harry just never believed. Of course there are the Lily theories, i.e., Snape is angry that Harry saw him call Lily a mudblood.
Despite his attraction to the Dark Arts and Voldemort's ideology of wizard supremacy, Snape's love for Muggle-born Lily Evans, Harry's mother, eventually compelled him to defect from the Death Eaters. He then became a double agent for Albus Dumbledore and the Order of the Phoenix.
Summary. As a character, Severus Snape was often misunderstood. Many believed he was a villain, and weren't convinced he was actually working for Dumbledore. Snape killed Dumbledore in an effort to protect Draco Malfo and spare him from the emotional trauma of murder.
Why did Snape hate Hermione? I think Snape was probably initially impressed with Hermione, but later frustrated with her, for a few reasons. Hermione was very book-smart and could come up with answers quickly, but didn't seem to be very good at improvising or trying to improve on existing Magic.
His father was neglectful and sometimes abusive, which may have contributed to Snape's disdain for Muggles. At some point during his school years, he decided to reject his father's name entirely, giving himself the moniker "The Half-Blood Prince" with his mother's maiden name instead.
James isn't motivated by anything much in attacking Snape in this way; he does it because he's bored, because he can, and because he wants to show off to some admiring girls, including Harry's mother, Lily. Harry is deeply disturbed by witnessing Snape's worst memory.
Snape having the same Patronus, the doe, as Lily symbolized his everlasting love and unwavering devotion towards her. He hadn't stopped loving her after their last altercation, marriage to James Potter, or death. She was his "always," his guiding light, and he protected Harry for her.
Why didn't Snape tell Harry he was protecting him?
Snape even said that he didn't want anyone to find out that he was protecting Lily's child, “especially Potter's son” (pg. 679 of Harry Potter and the Deathly Hallows) because of his hatred for James. Instead of providing Harry a safe haven from his abusive home with the Dursleys, he tormented Harry over an old grudge.
In the heat of the moment, Snape lost control and called Lily the forbidden word. He called her a mud-blood by accident because he was frustrated that lily did not like his closest friends. He did not mean it.
He promised to protect Draco Malfoy from harm and guide him whilst he attempted to perform the task the Dark Lord had asked him to do: to kill Albus Dumbledore. Snape was actually a double agent working for Dumbledore, who requested Snape to kill him anyway to spare him of a painful and humiliating death.
Having loved Lily all his life, Snape agreed to make amends for her death by acting as a double agent to keep Harry safe. He risked his life every day, as the slightest notion that he was betraying Voldemort would have had horrific consequences.
With effort, Snape was able to prevent Albus Dumbledore from learning the truth about his loyalties. Due to Snape's facade, Albus Dumbledore trusted Snape for reasons that were kept between them both until Snape murdered him.
By Harry Potter and the Deathly Hallows, it's a stretch to call Draco a villain anymore. We just watched — or read — him struggle to reconcile his choices and morals in The Half-Blood Prince. He can no longer justify his actions, and is far more aware of the evil he was born and raised into.
The movies follow the books closely enough that they aren't really separate universes, except for the fourth movie. There isn't any truly compelling evidence that Snape is Harry's father, because all the points you raise are explained. Snape hated Harry because Harry reminded him of the man who "stole" Lily.
Umbridge earns far more hate than Snape. While Gryffindors have to deal with Snape's biased behavior during potions class, Umbridge creates rules that affect all school life. Her educational decrees are constantly banning one thing or another.
He is simply awed by her and never hides how impressed he is. In the books, Harry never was attracted to Hermione because she was emotional, had average looks and hated his favourite sport, quidditch. He liked girls who were strong, beautiful and played quidditch.
For example, Lily Evans told her former friend Severus Snape that if he was going to refer to other Muggle-borns as "Mudbloods", then he had to use the term for her as well, not minding it much when he did so. Hermione Granger declared that she was proud to be a "Mudblood" in 1998.
Thanks to his own and Severus Snape's skills, Snape was able to hold off the curse from spreading, but it only gave him a year to live. Knowing that Voldemort had given Draco the task to kill him, and knowing that he would fail but not wanting his soul broken if he did, he asked Snape to do it instead.
Dumbledore was dying of a curse set by Voldemort, and only had a few weeks to live. If he died of the curse, that meant Voldemort had killed him and would get the mastery of the Elder Wand. If he killed himself, there was a possibility the Wand would still interpret that as Voldemort's victory.
For the second time in Voldemort's life, the unforgivable curse rebounded on him, as the Elder Wand wouldn't kill its master. Since Harry and his friends had already destroyed all of Voldemort's Horcruxes, this finally ended Lord Voldemort's life, with Harry finally defeating the Dark Lord.
