The Tales of Beedle the Bard/WMG

Death, from the Tale of the Three Brothers, is Der Tod from Elisabeth.
Death seems to be a Trickster when he gives the deathly hallows to the Peverell brothers. He claims the lives of the older two brothers after they use their gifts foolishly. Der Tod is the only Death I know of to reach this level of Jerkass.

Sirius isn't dead, but would be better off if he was. (He may also be Death... or a Death.)
When he fell through the curtain (in the book, anyway), he wasn't dead yet. Having passed into the land of death, he's become immortal; but he suffers constantly with an agony beyond a thousand deaths because physical bodies aren't made to cross over, just spirits. And he can never die. Ever. Like, ever ever, since the universe thinks he's already dead, and all three components of him (mind, body, and spirit/soul) are beyond the veil with all three still intact, and thus imbued with the power and eventually the attributes of death. It is for this reason that he may have become a death, or even, if he was the only one to cross the veil while no longer alive but not yet dead (going by the events of the movie), and considering that death is timeless, the Death shown in the tale of the three brothers. Aside from the total badassity of Sirius being the Death in the story, this leads to the next guess...
 * And remember, Sirius is constantly mistaken for the Grim in the early books- an omen which heralds death.
 * But then how would the Resurrection Stone have brought him back in the end of DH?
 * There is no reason being Death would prevent him from being summoned by the Resurrection Stone.

The core of the Elder Wand is a hair from the scalp of Death.
People assume that the Death in the tale of the three brothers was a skeleton, based on the most commonly used form in modern times as well as the skull in the drawing at the head of the chapter. This may be in error; Death is quite likely a relatively human-looking being. Wands typically have a core of something magical, typically a bit of a fantastic creature (hair, feather, heartstring). The book states that Death fashioned a wand from the branch of an elder tree; it doesn't say how, and no mention is made of the core. This not only allows any fatal spell to be blocked and fatal spells cast by the wand to have that extra "kick," but also means that the wielder carries death with him in a more literal way than the average mortal. Hence, why people with the Elder Wand tend to die gruesome deaths even when they aren't being boastful about their super-fancy deathwand.
 * Word of God says that the Elder Wand's core is a Thestral tail-hair - so close, but not quite. And people interpret the whole "Death himself forged the Wand" thing LITERALLY?
 * Why not? This is a universe with wizards and witches, centaurs, phoenixes, basilisks, vampires, werewolves, accurate prophecies, soul-sucking demons, and an afterlife - is it so much of a stretch to believe that there might be a personification of death?
 * Let's just say that the core is Sakura's feather. ...Hey, somebody had to say it.
 * Jossed. J. K. Rowling said on her website that it was a Thestral hair, though if the below theory is correct, then this theory lives on to another day!

Death is a Thestral.
Or rather, all thestrals are literal personifications of Death.
 * And they only bless people who have seen their collective form, see their individual form.

Death is a Thestral Animagus.
An invisible creature that is strongly associated with the afterlife... sounds like Death. So, when the Peverells made the bridge, and Death created the hallows, he used one of his tail hairs to make the Elder Wand, transferred the invisiblity factor of the Thestral to his cloak, and used some random rock for resurrection stone, maybe a brooch or cut gem.
 * Death is a shape-shifter who can take ANY form.

The Elder Wand can only be defeated by The Power of Love.
How come Dumbledore was able to defeat Grindelwald if Grindelwald had the elder wand? Every other time the wand changed hands, subterfuge is involved; yet Dumbledore appears to have defeated Grindelwald in a standard duel. If Word of God says that Dumbledore was attracted to Grindelwald, it must be the only explanation. After all, Dumbledore knows a lot about The Power of Love when he talks about Harry's mother, so he must have had experience with it somewhere.
 * Then how come Dumbledore doesn't have a lightning-bolt scar on his forehead?
 * Who said it has to be a lightning bolt on the forehead? He has the map of the London underground on his knee, remember?
 * Rowling said Grindelwald "conjured a white handkerchief from his wand". So, um, maybe it wasn't Dumbledore's magical talent that won the battle?
 * Um, wasn't that Rita Skeeter saying that's what could have happened?
 * Grindelwald lost to his other wand.
 * My theory is that the wand defends its owner from attack, but not itself from capture -- Dumbledore defeated Grindelwald with a simple Expelliarmus. (Rowling clearly loves that spell -- it's what Harry used to win both his duels with Voldemort.
 * But didn't Lupin say in DH that Expelliarmus was a very unusual spell to use in the first duel?
 * Worked for Harry, didn't it? Under some circumstances, the most unusual, least expected move can be the thing that makes all the difference in a fight. Both Malfoy and Harry were able to use the spell in a duel with the wand owner involved, and it worked. Apparently the disarming spell is a loophole since it is not dueling per se any more than shooting the gun out of your opponent's hand is really and truly engaging him in a duel of pistols. You're participating in any sensible definition of the term but you're still not playing by the rules of what's supposed to constitute the actual fight.
 * It's simple. The Elder Wand isn't invincible. Indeed the one consistent feature in the Elder Wand's history is that every single one of its owners is defeated and loses it. It has changed hands many more times than directly mentioned in the novels, and undoubtedly some, if not most of them, occurred in direct duels. The Elder Wand is just an unusually powerful wand, the user's own skill still matters. A sufficiently powerful opponent can overcome whatever advantage the Elder Wand gives. Dumbledore beat Grindelwald because he was just that good.

The Resurrection Stone builds a "ghost" based on the user's memories.
Like how Priori Incantato and the Priori Incantatem effect create a shadowed image based on the effect of the most recent spell, or an imitation of the most recent people affected by a killing spell from that wand. The only difference is that the Priori Incantatem effect takes the image from the residue or backlash or whatever of the person's actual soul, but the Resurrection Stone uses as a reference the caster's memories. this is why the beings made by the resurrection Stone turn out to be extremely two-dimensional, but the shadows from Priori Incantatem are properly fleshed out and possess knowledge and habits that the people involved in the spell did not necessarily know about.
 * The only problem with this is that Sirius is "younger by far than Harry had seen him in life", as is Lupin. This suggests that they are being presented as they were in the prime of life, rather than how they were when they died (necessarily). If they were created from Harry's memories, they would have looked how they looked when he knew them.

The Elder Wand was made from a branch of Yggdrasil.
With the tree of life obviously representing life, and the thestral tail-hair representing death, the wand is a paradox. This may explain why it is so capricious.
 * Askr Yggdrasils, the ash tree?
 * oops... I must have overlooked that part...
 * What if by elder she simply meant old, rather than specifying the type of tree it was made from? The book says "so Death crossed to an elder tree on the banks of the river." As Yggdrasil is indeed quite old, it qualifies as being called an elder tree, even if it is not part of the Sambucus genus.
 * Except Deathly Hallows explicitly mentions the wizarding superstition "wand of elder, never prosper," with that referring to the type of wood. Also note how the wand's decoration appears to be elderberries.

The Elder Wand's duel-winning power only applies when it is being used with the intent to kill
If the Elder Wand is just a +1000 wand, then we must conclude that Dumbledore is vastly more powerful than Grindelwald, having won a nigh-unbeatable wand from him, and that Voldemort is vastly more powerful than Dumbledore, having dueled him to a draw. And that's no fun. So, we assume that its true power only arises when one intends to kill, and draw the reasonable conclusion that Grindelwald was not dueling to kill, then everything makes sense again!
 * When did Voldemort ever duel Dumbledore to a draw? As far as I know, they never actually fought at all.
 * I believe they dueled in the fifth book.

Neville is the master of the Elder Wand.
They were wrong about which way the split in the Elder Wand's control went, and it went Snape-> ->Neville. Nobody said it had to be a wizard to control the wand, and for bonus points, the presumably first non-human to control it was also female.
 * Um... The book very clearly explained how the Elder Wand changes masters. At least, it was pretty clear to me. In case it wasn't, here it is: In order for the Elder Wand to recognize a new master, its current master must be defeated, but "defeated" does not mean "killed". It could mean something as simple as Disarming, as  did to the real master of the Elder Wand as of the end of Half Blood Prince,   (also: the master doesn't have to be using the Elder Wand for it to be defeated). So there's the first link in the progression broken: Snape was never the master of the Elder Wand, because  . The second link in the chain has a very low probability of being able to mutter an incantation (she'd have to hold the wand in her mouth, and proper word choice and pronunciation is kind of a big deal in the Potterverse), and she never defeated any of the wand's true masters. Neville, while taking a level in badass, also never defeated any of the wand's masters, but hey, come on. He ended up being master of a big fucking sword that can only be mastered by a true Gryffindor; he's no less Badass for not being a master of the Elder Wand (which, as   pointed out later, is a lot more hassle than most people want to deal with).
 * The point was, there was a lot of confusion with that, and even with Word of God the subject is a Base Breaker. The premise of the guess follows the beliefs of the group who believes Snape was at one point the master to its logical conclusion. And the guess specifically stated that it never specified that the wand's master had to be human. The ability to speak Canis Latinicus follows from having human-like vocal abilities.
 * Also none of this reasoning is consistent with ; after all the number of scenarios where the wand could possibly switch masters is endless. One of Harry's  could playfully disarm him, or a muggle could steal his wand, etc, without the Elder Wand ever.
 * It doesn't have to be consistent - Harry's not that bright and has never paid attention to magical theory (at least that's my Watsonian explanation for it never being explained).
 * It doesn't work like that. Whether or not a wand changes allegiance has a lot more to do with the intent of the "defeat" than the actual act of disarming your opponent. If you're just fooling around or practicing or something, the wand stays with its rightful owner. If the wizards or witches are duelling with a serious, perhaps life-or-death intent to win, then the wand would change hands. Remember, wands basically have feelings here--imagine them as a shallow girlfriend who will go off with whoever seems to have the most power. It's not as simple as another boy simply yanking them away.
 * I would like to point out that being a Gryffindor does not necessarily get you the sword, acts of valor do.
 * To clarify everything here, Harry is clearly the master of the Elder Wand  because if he was not then expelliarmus would not have worked against the killing curse. Also Harry did not master the Elder Wand with his own wand he did so when he took   wand from him physically, thus even if he is disarmed in a real duel it would be his holly and phoenix wand and not the Elder Wand which is in Dumbledore's tomb. The only way for him to lose the mastery of the Elder Wand is if he is killed because of the way he obtained the mastery over it, because I sincerely doubt he uses the wand that he used to defeat the Elder Wand.

The Resurrection Stone is made from...

 * Obsidian- which is associated with the underworld.

Asha from the fountain of Fair Fortune is a Werewolf.
She's sickly, nothing can cure her, and she's totally the woobie.
 * Strangely enough, i can totally see that.
 * And Altheda was the one who really invented the Wolfsbane potion!
 * Asha fell very ill during sunset, and wouldn't allow anyone to touch her. It was moonrise at the same time and she didn't want to hurt the others. Brilliant!

The river in the Tale of the Three Brothers that Death crosses for the Elder wand is not the literal river that the brothers tried to cross, but a metaphor for death.
Where else would Death get the styx to carve into the most lethal wand in all of existence? But puns aside, a wand from a tree beyond the veil would probably be much more potent, and definitely more resistant to "dying" from violence or old age (again), than would a wand carved from a normal (albeit very, very old) tree.
 * The tree itself doesn't have to be more resistant as long as it's Death himself who carves it.

The river in the Tale of the Three Brothers is a metaphor for death.
Not a literal example within the story of dying by falling into a literal river; Death probably wouldn't have cared that some random wizards thought to build a bridge and escape his grasp if fate is that easy to fight. Other wizards would likely have escaped his clutches many times if that was the case. However, if each brother used their magic to circumvent their destined deaths in much more ingenious ways, he might then choose to intervene.

The Tale of the Three Brothers is real.
Sure, Xenophilius offered the alternate theory that the three brothers were just very powerful magicians who made their own cloaks and wands and rings, but it doesn't quite gel with what we know about the magic in the series already.

1. The Elder Wand: We've been told time and again that wands are only as good as the wizard who uses them, and the real power comes from the wizard who wields the wand. So why suddenly is there a wand which miraculously makes peoples' magic stronger? Unless there's something about crafting wands which was forgotten in the hundreds of years since the Elder Wand was made, then it has to have come from somewhere else, and since it couldn't have been another wizard, Death is as good an explanation as any.

2. The Ring: This is literally the only item we've come across which can do this. The Priori Incantatem spells are after images of old spells, Voldemort's appearances are all linked to his soul, because he wasn't really dead, so where exactly does this ring come from? Who has the power to bring people back from the dead, even as some sort of after-image, that stays permanently? Death. The Ring makes people stay until the user wants them to go, Priori Incantatem only lasts for as long as someone's wand is pointed at yours.

3. The Cloak: Again, we're told repeatedly that invisibility cloaks either don't make you truly invisible or don't last forever, so why is there one that makes you completely invisible and has lasted for hundreds of years?

The gist is that there must be limits that human wizards and witches can't surpass when it comes to magic, no matter how skilled they are. If Dumbledore, Grindelwald, the founders of Hogwarts and more haven't been able to replicate the efforts of three wizards despite thousands of years of magical improvements, then where did these three items come from? The story of the three brothers meeting Death must be true, there isn't another explanation.


 * Pretty much confirmed in-universe when Ron mentions that the Invisibility Cloak acts exactly as the tale describes, then Harry puts it together that he's descended from the third brother. (This becomes Hilarious in Hindsight when you realize that Harry and Voldemort are pretty much cousins seventy-times removed since Voldemort is descended of the SECOND brother) And then Dumbledore and Voldemort flat out prove the Elder Wand is real so the first brother also existed. Harry even proves the Stone is real when he uses the thing to summon his parents, Sirius, and Lupin. Since we know Voldemort's grandfather claimed direct lineage to the Peverell brothers as stated in book six and that there were three of them...well, do the math. The Peverell siblings are the three brothers in the tale and their encounter with Death happened.

The real reason Harry survived Voldemort's curse that destroyed the Horcrux within him was his mastery of the Deathly Hallows.
If the Deathly Hallows are real, then by the end of the book Harry is the master of all three - 1)He has earned and found and was the last person to use the Resurrection Stone, and even had the phantoms of his loved ones as created by the Stone with him when he was killed. 2)He owns and has in his possession the Invisibility Cloak, also given to him by Dumbledore and inherited legally from his father. 3)He has, according to the events later in the book, mastery even if not possession of the Elder Wand, which was also the wand used to kill him.

Thus he is the mastery of all 3 Hallows and according to the legend the master of Death itself. Voldemort's curse didn't kill him because he could not die. He then revokes his mastery when he rejects the Wand consciously later, presumably.

This also means that Dumbledore also had all 3 Hallows at some point, but I think not all at the same time, and he had only borrowed the Cloak.


 * I love this theory because it's somewhat less far-fetched than some other dei ex machina involved in the final battle, and because it's totally consistent with Dumbledore's character: with all three Hallows, he found himself Master of Death and became afraid of his own power, because he knows what the darkness inside him -the one that believed in "the greater good", the one he keeps fighting against- is capable of; and thus gave one of the Hallows to Harry as soon as he can. Of course, James' will helped him to regain his reason, but I like to imagine him tempted.
 * In this theory, either he found the Stone shortly before Christmas 1991, or had been Master of Death for quite some time at this point and only "accepted Death as an old friend" during this very year, after considering Voldemort's mistakes and/or talking with Flamel -becoming the Dumbledore we all love only at the beginning of the saga.

Harry Potter was never the master of the Elder Wand.
Draco Malfoy was the master, wand ownership transfers only with magical defeat, and perhaps also non-magical murder in the case of the Elder Wand, but not via physical wand grabbing.

So why did the Elder Wand not kill him? Because it was facing another wand also owned by its master. It was Draco's wand vs. Draco's wand, and the Elder Wand realized that first (It seems more sentient than other wands) and gave up.

In the movie continuity, Neville is the master of the Elder Wand.
Warning: spoilers for Deathly Hallows, Part 2.

DEATH belongs to Slytherin House

 * DEATH cannot see through Harry's cloak. DD, Moody, Crouch, Norris and such Gryffindors can see through. The Cloak only works versus children, squibs and Slyths.
 * Out of all the people you mentioned, only DD is a confirmed Gryffindor. Also, Mrs. Norris is a CAT.
 * Slytherins do not even know that there is such a thing as an invisibility spell. POA cloaked Harry attacks Draco. Draco automatically assumes that it is ghosts, he never considers for an instant that the attack is from a Wizard with an invisible spell.
 * DH: Ministry hunts Harry, they never think of putting anti-invisible Charms on the Ministry and Gringotts and the Secret Thaumonuclear Bunker.
 * Gryffs can see through the Cloak; Slyths don't even know that invisible spells exist, so they never bother to check. The Cloak works against DEATH, therefore DEATH is a Slytherin.
 * Draco knew about invisible spells in HBP, but he was sorted too soon. DH ends with the Malfoys being redeemed because of random wand rules, therefore they became Gryffs.
 * Slytherin =/= evil. Besides, despite their apparent Heel Face Turn (or rather, they went from working for the Big Bad to being neutral), Malfoy was still somewhat of a coward, although also somewhat intelligent - he was implied to be able to pick up new skills rather easily. Of course, all of that talent was hidden under his Jerkass personality and a laundry list of other character flaws. If he had been sorted anywhere else, it probably would have been Ravenclaw.

The Elder Wand is a Horcrux of Antioch Peverell.
I, of course, express skepticism that the Peverell brothers actually met Death after crossing a deadly river. It is my opinion that Antioch crafted the Elder Wand, but was having issues with controlling it, as Thestral hair is very difficult to incorporate into a wand. Seeking power and control over the wand, Antioch murdered the rival wizard with the immature wand, and used the murder of his rival to seal a piece of his own soul into the Elder Wand. Euphoric from the new found power of the wand, Antioch went to the bar bragging of how he bested death (by placing his own soul into his own wand!), but did not count on being killed by non-magical means. Without any loyal followers to restore his body, his soul fragment lives on in the wand, accounting for its power, the ability to do magic considered impossible, and the unusual characteristic of transferring loyalty to the wizard who overpowers the previous owner.
 * But then, why was Harry able to  so easily, unlike Voldemort's many Horcruxes?
 * Because he was never resurrected? Also, I think he only destroys it in the movie.

The Veil in the Department of Mysteries is the last of Death's mortal presence.
The stone dias is the last remaining piece of the ancient bridge the Peverells made to cross the river Styx (obviously related to the above WMG about the river). Somehow, somewhere down the line, he was caught by the Wizards' Council, and with a complex series of spells, trapped between the realms of the living and the dead, leaving only the last of his tattered veil. The Department of Mysteries, and consequently, the Ministry of Magic, was developed to keep an eye on Death's cage, and scientifically benefit from this hole in reality.