At the end of the series, Dumbledore admits to
1 He Asked Snape to Kill Him
Having first used Snape's grief to manipulate him into a lifetime of servitude, Dumbledore then effectively sentences him to death by attempting to have him become the master of the Elder Wand.
Dumbledore takes care of his duties; he even refuses the leadership role that's briefly presented to him during the Walk of the Qilin ceremony. Although he had become close with Jacob during the adventure, Albus stays outside of his muggle friend's bakery during the wedding.
I would say his biggest mistake was not finding closure for his family. If he had come to grips with his role in Ariana's death, he would have done more against Grindelwald. In the Deathly Hallows he said: “But while I busied myself with the training of young wizards, Grindelwald was raising an army.
1 Lord Voldemort
Lord Voldemort is the scariest villain in Harry Potter, if only because he is the series' overreaching villain who successfully evades death more than once.
Draco Malfoy's mother Narcissa was cold, cunning and devoted to the Dark Lord. But she was also a mother, which meant she was willing to risk everything to make sure her son was safe. When Harry survived Voldemort's Killing Curse for the second time, Narcissa pretended he was dead so she could get to Draco.
Lucius Malfoy had a strong dislike of Albus Dumbledore. This is due to two reasons – Dumbledore believed in Muggle rights which contradicted Malfoy's pure blood beliefs. In addition, Lucius was a Death Eater, so he believed that Lord Voldemort was a much more powerful wizard than Dumbledore.
He has grown afraid of Harry's connection to Voldemort. Perhaps Voldemort, knowing Dumbledore's love for Harry, would possess Harry and provoke Dumbledore to kill him. So, Dumbledore attempted to avoid Harry throughout Book 5 for Harry's own good.
When he and Gellert Grindelwald made plans to subjugate Muggles and take power in the Wizarding world, Albus planned to bring Ariana with them, but Aberforth pointed out that she was in no state to go. This launched a three-way duel between the brothers and Grindelwald, and Ariana was accidentally killed in the fray.
For all intents and purposes, this act only solidified Harry's suspicions that Snape was working against Dumbledore the entire time. But there were parts of the story Harry didn't know, including that Dumbledore was already dying and had asked Snape to kill him when the time was right.
Dumbledore and Grindelwald took a blood oath to not fight each other. "Fantastic Beasts: The Crimes of Grindelwald," the second film in the series, reveals that as teenagers Dumbledore and Grindelwald undertook a blood pact that wouldn't allow them to move against each other.
Following Lord Voldemort's defeat at the hands of her student Harry Potter and the deaths of Headmasters Albus Dumbledore and Severus Snape, McGonagall takes the position of Headmistress.
Dumbledore reveals how thoroughly he loves Harry. Harry is brave, and Dumbledore is proud as any father would be. More than that, Dumbledore succumbs to a parent's weakness; he cares more about Harry's happiness and wellbeing than the wizarding world he is trying to protect.
The betrayal here stems again from the idea of "For the Greater Good" – Dumbledore seems to have chosen Harry to die, since he had already been chosen to die once, in order to save the rest of the world… he just never informed Harry of this decision. Whoops.
Now, as firmly established, Snape was not the greatest fan of Harry, but that didn't mean that he ever stopped loving Lily. Dumbledore was surprised that Snape seemed to care for the boy. With a swish of his wand, Snape conjured up a Patronus – Lily's Patronus, a doe. 'Always,' he said.
Dumbledore knew that destroying Voldemort's horcruxes was the only way to truly defeat him. He believed that Harry was the one person who was smart, courageous, and perhaps lucky enough to find and eliminate all the horcruxes.
Dumbledore had to keep certain things hidden from Harry just in case Voldemort read his mind. He did not want Harry knowing that Snape brought the sword of Gryffindor for that reason, it is very likely that he did not want Harry knowing that he planed to have Snape kill him for the very same reason. Save this answer.
He finds out for sure immediately after Nagini's attack on Arthur Weasley. This night is significant in many ways. While Harry sleeps, he enters Nagini's mind.
In the sixth book, Dumbledore dies when facing Severus Snape on top of the Astronomy Tower, as Harry helplessly watches from concealment.
It was Snape who overheard the prophecy that would go on to define Lord Voldemort and Harry Potter's lives for years afterwards. The prophecy can be seen as the catalyst for everything; it led to the death of Lily, his great love, and Snape spent the entire course of Harry's (and his own) life trying to make amends.
The Malfoys are able to avoid serving time in Azkaban, as they provide evidence that helps the Ministry track down the Death Eaters who had fled after the war. It is also probable that, since Narcissa's lie to Voldemort saved Harry's life, the family is pardoned for their crimes.
Fenrir often spoke about how his favorite targets were children, and he even killed students during the Battle of Hogwarts - including Lavender Brown. Fenrir was a soulless killer who used carnage for personal gain. Fenrir was a terrifying antagonist who fans despised.
Without a doubt, Dolores Umbridge is the most hated character in the Harry Potter universe. Her unnaturally calm and polite demeanor paired with her cruelty makes her incredibly irritating.