JKR: I see him [Dumbledore] primarily as someone who would be self-taught. However, he, in his time, had access to superb teachers at Hogwarts, so he was educated in the same way that everyone else is educated. Dumbledore's family would be a profitable line of inquiry, more profitable than sweet wrappers. - Emerson and Melissa's Interview with JKR
There you have it, friends - straight from the author's mouth. Dumbledore's family is something we should be asking about if we want clues to the ending of the series. So, let's pick up this line of inquiry, shall we? Let us work together to see what profit can be made from it. Following are some ideas about what JKR might be driving at, and a way that some aspects of the series that are currently loose ends might be tied together to form a few answers.
The only member of Dumbledore's family that I recall being mentioned throughout the books is Aberforth Dumbledore, Albus' brother. Aberforth is, according to a JKR answer at the Edinburgh Book Festival interview, the bartender at the Hog's Head Inn. He got into some trouble with the law for performing inappropriate charms on goats. He was in the original Order of the Phoenix, though Moody only met him once, and we have no idea what he was doing for the Order. Dumbledore has broadly hinted that Aberforth provided him with regular information about various goings on in the Wizard world. He was seen in Hogsmeade with Mundungus while the latter was pilfering goods from the Black family home. And he was at his brother's funeral. It may be important to note that, though we obsessive readers have made the link between Albus and Aberforth, Harry has not yet done so. One pivotal moment of Book Seven will most likely be a major reveal of this information to Harry. How will Harry react to learn that his beloved late Headmaster has a living relative? And what sort of relationship might he form with Aberforth? JKR has strongly hinted that we'll get to know him better in Book Seven. Is Aberforth the profitable line of inquiry?
As to Dumbledore and his early life, what we know is pretty much limited to what JKR writes, above. Unfortunately, none of what we know really touches on Dumbledore's family ties. In fact, all mention of the Dumbledore family is conspicuous by its complete and utter absence from the series. Without JKR's comment, above, this might mean nothing. Perhaps Dumbledore's family simply isn't pertinent to the story. However, we now know that isn't the case. So, if they are important, why have we heard absolutely nothing about them?
Apart from Dumbledore's lack of family, we have a few solid facts about his major accomplishments and activities. We know that he met Nicholas Flamel at some point, and he worked with him on Alchemy. We know that he somehow acquired Fawkes, the Phoenix. He discovered the twelve uses of Dragon blood. He was the Transfiguration teacher at Hogwarts before he was Headmaster. And, in 1945, while he was already a Hogwarts professor, he defeated the dark wizard Grindelwald.
The First Dark Lord
Grindelwald seems to be one of those loose ends in the HP series. Why is he there? We don't really need his defeat to prove to us that Dumbledore is a magnificent wizard. Why did Dumbledore feel compelled to be the one to defeat Grindelwald and how did he do it? Perhaps the answer can be found in another question: why does Harry feel compelled to defeat Voldemort? Dumbledore helps him to see why in HBP. He helps Harry to realize that, Prophesy or no Prophesy, Harry would never be able to rest until Voldemort is stopped. Why? Because Voldemort killed Harry's family. Further, Harry has spent the last several years watching Voldemort continue to wreak havoc everywhere he goes. Harry has watched those he cares about suffer and die because Voldemort is who he is. Dumbledore is a wise man, and this isn't the first time that he sees deeply into someone else's motivations and drives. Could this also be a clue that Dumbledore and Harry share a certain kind of family history?
Torment in the Cave
What torment was Dumbledore put through in the cave with the green potion? I've read a few ideas, but mine is slightly different. Let's recap what Harry sees and hears while Dumbledore is drinking the foul potion:
After the first goblet, Dumbledore's eyes close. He drinks three goblets of potion. He staggers, halfway through the fourth, and falls forward against the basin. His eyes are still closed, and he is now breathing heavily. His face twitches "as if he was deeply asleep, but dreaming a horrible dream." (Harry has been tormented with horrible dreams and visions several times, and they usually involve his mother's screams and flashes of green light.) He begins to lose his hold on the goblet, and he begins to pant. Then he begins to speak in a voice that Harry does not recognize. The voice is filled with fear. As Harry follows the Headmaster's orders and pours the potion down his throat, this is what Dumbledore says:
"'I don't want... Don't make me...'
'...don't like... want to stop...'
'I don't want to... I don't want to... let me go...'
'Make it stop, make it stop.'
'No, no, no, no, I can't, I can't, don't make me. I don't want to...'
'It's all my fault, all my fault Please make it stop, I know I did wrong, oh please make it stop and I'll never, never again...'
'Don't hurt them, don't hurt them, please, please, it's my fault, hurt me instead...'
'Please, please, please, no... not that, not that, I'll do anything...'
'No more, please, no more...'
'I want to die! I want to die! Make it stop, make it stop, I want to die!'
Dumbledore is progressively described as moaning, groaning, sobbing, cowering "as though invisible tortures surrounded him," shaking from head to foot, screaming, hammering his fists on the ground, yelling and screaming in anguish before finally rolling over onto his face with a rattling gasp.
It was a hard scene to read, I thought. It was disturbing to see the steady, powerful Headmaster so reduced and helpless. I have heard various explanations for Dumbledore's words and anguish: he felt remorse over his mistakes with Harry, or over the Potters' deaths, the potion caused a sort of Super-Cruciatus Curse, etc.
The thing that stood out to me was that his voice sounded so different to Harry, so frightened. And his words gave me the impression, not of a grown, 100-and-some-odd year old Dumbledore having regret over the Potters' deaths, but of a small child being severely punished or tormented. And I got the impression that the child was being forced to do something and witness something that caused him extreme guilt, shame and horror. I got an image of young boy Dumbledore, watching his own family tortured and murdered by another very dark wizard: Grindelwald. It's true that all of the pleas of "stop" and "don't make me" could refer directly to the potion: "stop making me drink this horrible stuff!" But I think it's more likely that it refers to the visions in his head. I think that he was being made to watch something horrible, and that he had either been tricked or forced into doing something that may have contributed to the horror. He is trying to stop someone else from being hurt, and he blames himself for the situation. In true Gryffindor fashion, he tries to take the threat onto himself and help whoever is being hurt. Some of his pleadings suggest that he, too, is being physically hurt, along with those for whom he shows such selfless concern. The scene escalates to the point where he no longer believes that he can bear what is being done either to him or this mysterious "someone else" and begs to be released from the nightmare with death. Who, before Voldemort, would have inflicted such a ghastly nightmare on another? Who but another very vicious, dark wizard?
Who was Grindelwald? My penchant for checking on name meanings gives very little information: I have found the word "grindel" translated roughly to "standard" in English, and, in another dictionary as "plough beam." The family name Grindel is defined as "one who lives by the moor or the swamp." "Wald" means forest. So, will something of interest happen "in the forest by the moor?" Was Grindelwald defeated near a standard, swampy forest with a good whack from a plough beam? I highly doubt it. More likely it is a name meant to signify darkness, hidden qualities, murkiness and lack of clarity and light. In essence, Darkness.
There has been a lot of focus in the world of endless HP speculation about the coincidence of Grindelwald's defeat coming at the same time as the end of Muggle WWII: the fact that the name is German, possible relationship to Hitler, etc. I suppose it is all possible. JKR has said that strife in the Wizard world can and has spilled over into the Muggle world. The timing coincidence that I find more interesting, however, is the fact that it happened at the same time as Tom Riddle's coming of age. In 1945 Tom Riddle was Head Boy at Hogwarts (using the Lexicon timeline), and Dumbledore was already a teacher there. I find it too much of a coincidence that Dumbledore's defeat of Grindelwald and the completion of Tom Riddle's education coincide so closely. Of course, every time I think that way, I remember those who were caught in the infamous "Mark Evans Scandal," and wonder if, perhaps, I should find another hobby. Still the dates are interesting, no?
I think it's possible that Grindelwald's reign of terror (of which we have heard very little) involved the killing of most of Dumbledore's family, that something about how that happened left the young Dumbledore filled with guilt and horror, and that this is the nightmare he relives in the cave. From the tone and choice of words that the Headmaster uses, I think it happened when he was a child, but older than Harry was when Voldemort killed James and Lily. Dumbledore was old enough to understand, to feel responsible and to plead for it to stop, but not old enough or powerful enough to fight it.
If Dumbledore's family members were victims of Grindelwald in a way that left him particularly scarred (and I'm speaking of emotional scarring - though I suppose this could be the origin of that map of the London Underground above his knee!), it is easy to see why it fell to him to take on Grindelwald. Though many people have been killed by Voldemort, the particular circumstances of Harry's parents' deaths create the opposition between him and Voldemort, and foist Harry into The Chosen One position. I believe that something very similar happened to Dumbledore. I'm not suggesting an exact mirror of Voldemort's first downfall when he tried to kill Harry. Instead, I see some special targeting of Dumbledore and his family, and something that stopped Grindelwald from killing Albus and Aberforth.
How did Aberforth escape the fate of his family? Was he younger, and managed to remain hidden? Perhaps he was out playing with the goats? Does the fact that Aberforth is generally perceived as "a bit odd" have something to do with what he witnessed or what he suffered? Why wasn't Albus killed as well? Did he have some specific protection, such as something similar to Harry's situation with Lily's sacrifice? Or, was Grindelwald interrupted in a way that forced him to leave the job unfinished? We can only speculate. However, if this theory is correct, Albus would have grown up with a horror that is at least as nightmarish as Harry's memories, and a motivation to stop Grindelwald that would have been at least as fierce as Harry's own drive to defeat Voldemort. Was this part of what also motivated Dumbledore to become such an extraordinary student (remember Professor Marchbanks' reflections about his extraordinary NEWT results?), and, ultimately, the most powerful wizard of his generation?
JKR tells us that Dumbledore had excellent teachers, but was mainly self-taught. She doesn't mention talented parents, or having grown up in a powerful magical family. Were they targeted by Grindelwald before they had a chance to teach their sons magic? Were they wizards? Were there other siblings killed?
Dueling Dark Lords
In order for Dumbledore's family to be a "profitable line of inquiry," it must have some bearing on the outcome of Book Seven. So what is the connection? Perhaps it has something to do with Voldemort and Grindelwald?
Tom Riddle left the orphanage in his sixteenth year to find his family. What else did he find? Did he, at some point, hook up with Grindelwald? How active was Grindelwald when he had power? We don't hear much about if or how he terrorized the Wizarding population. He would have been in power during the years that Tom Riddle, Hagrid, and even McGonagall were students at Hogwarts. Could Tom have sought out the reigning King of Darkness to get information or instruction that he couldn't get at Hogwarts? Did Grindelwald teach Tom Riddle something before his defeat? Something that Slughorn couldn't teach him? For instance, how to make those Horcruxes? The magic is so very dark that not even books in the restricted section speak of it. Where did he learn it?
But, if Grindelwald knew about Horcruxes, and was such a dark wizard, why didn't he use them himself? Or did he? Is that why Dumbledore has a hunch about what Tom Riddle did to become the "immortal" Lord Voldemort? Remember, in HBP, Dumbledore tells Harry that he considered Harry and Ginny's encounter with the diary proof that Voldemort had split his soul. This was not the first time that Dumbledore had considered the possibility - it was the proof that his suspicion was correct. This suggests that he had believed it was possible for some period of time before that. Is that because Grindelwald had used the technique before Voldemort, and Dumbledore was the one to destroy Grindelwald's Horcrux before defeating the dark wizard himself? Dumbledore believes that no one else had made multiple Horcruxes. He does not say that he is unaware of anyone else making a single Horcrux.
If Dumbledore defeated Grindelwald because of a violent and tragic family history, Aberforth may be the only living person to know the story. If the story involves finding and destroying a Horcrux, it could be, indeed, a profitable line of inquiry. Additionally, the knowledge of Aberforth's connection to the late Headmaster might salve some of the regrets that Harry felt at Dumbledore's funeral. Harry realized that there were so many things he didn't know about Dumbledore, and now, he believes, he never will. I believe that there will be a comforting surprise waiting for Harry when he learns that there is someone who has the answer to some of these questions.
Of course, if this theory is correct, then many, many years went by between the killing of Dumbledore's family and the defeat of Grindelwald. According to the Lexicon timeline, Dumbledore would have been somewhere around 100 years old when he finished Grindelwald. I hope it doesn't take Harry that long to take care of Voldemort... Then again, come to think of it, that would mean a lot more Harry Potter books, wouldn't it? Alas, we know that the series must be wrapped up in Book Seven, though we can't be absolutely certain that means it will all be finished in year seven. The book could conceivably take more or less than a year, but I suspect it will follow roughly the same timeline as the others. Harry will have to act quickly. He will need much help, from many sources. Will Aberforth have his own memories to add to Harry's collection?
While I realize the above is rife with pure speculation, I believe it offers a plausible explanation for all the facts, and may shine some light on the importance of Dumbledore's family.
Poor old Snuffles. He must really like you Harry... imagine having to live off rats.
Ron Weasley Goblet of Fire, Chapter 27, Page 534
Quidditch started in the 11th century at a place called Queerditch Marsh, which is not marked on muggle maps because wizards have made the place unplottable. Originally it was quite a crude game played on broomsticks with just the quaffle.