Harry Potter: Dumbledore Officially Has The Most Disturbing [SPOILER]
In the "Harry Potter" series, boggarts play a pivotal role, especially in the third installment, "Harry Potter and the Prisoner of Azkaban." These magical creatures are some of the most terrifying in the wizarding world because when faced with a witch or wizard, they will transform into the one thing they fear the most. Boggarts are first introduced in Remus Lupin's classroom, and it is revealed that Harry's greatest fear is Dementors. Throughout the series, we learn other characters' fears — Molly Weasley sees the corpses of her family and Harry, Hermione Granger must overcome a failed exam, and Ron is faced with a spider — but we never see how a boggart takes shape when faced with the seemingly fearless Albus Dumbledore.
Author J.K. Rowling was asked about this topic during a live web chat hosted by Bloomsbury in 2007. She answered that Dumbledore would also see a corpse, but it would be of his sister, Ariana. Though her demise is briefly mentioned in the movies, she is an important part of the headmaster's life. Following a disagreement between the Dumbledore brothers, Albus, Aberforth, and Gellert Grindelwald engage in a three-way duel. Unfortunately, Ariana gets caught in the crossfire when a stray spell strikes her and ends her life. No one knows which wizard killed her, and Dumbledore lives with the guilt that it might have been him. As a result, if he were to come across a boggart, he would see her lifeless body and wonder if he had been the one to hurt her.
Dumbledore's boggart reminds him of his failures
Though it can be argued that Molly's boggart is far more traumatizing — it's not easy seeing the bodies of your loved ones lying on the floor — Dumbledore's is actually the most disturbing. What Molly sees is merely a fear of what may happen since Voldemort has risen back to power and another war is on the horizon. Dumbledore, on the other hand, has already seen his sister's corpse. He has already lived the trauma of watching Ariana die. Seeing her body again, even as a boggart, would not only be horrifying but also bring up all the memories of that fateful day, which some believe should've been depicted in "Fantastic Beasts." In the end, he has lost his sister — whom he can't be sure didn't die by his hand — and he has caused an irreparable rift between himself and his brother.
Furthermore, it's important to consider the Mirror of Erised. Though Dumbledore tells Harry he sees himself holding socks, he actually sees his family, together and happy, according to J.K. Rowling in that same web chat. (Of course, in "Fantastic Beasts," he sees Grindelwald instead.) Because this image is what he wants most in the world, it only makes his boggart even more awful. Seeing Ariana's lifeless body is a heartbreaking reminder that, in his mind, he is at fault for his family's downfall, and he will never move on from that, even in death.