The wood from one tree and one tree alone, an ancient White Oak, would bring death to an Original Vampire. When the tree burnt, all hope was thought lost. But the ash from the tree was saved and Witches forged a dagger which the ash could be bonded. This alchemical bond provides the necessary poison. It must be brandished by Humans alone for it would bring death to all Demons who wield it. As long as the dagger stays in place, the Original, for all intents and purposes, is dead.
The White Oak Ash Daggers are weapons which were forged by witches as a means of subduing the Original Vampires. This acts as a balance in Nature so Humans can fight them, since the White Oak Tree was burned down, leaving no weapons to permanently kill the Originals. If dipped in the ashes of the White Oak Tree, dating from the genesis of the vampire race, and placed in the heart of an Original Vampire, they remain dead for as long as the dagger remains in the Originals heart.
The daggers must be used only by humans, because if it is wielded by a monster - which refers to any Non-Original Vampires and possibly Werewolves - the dagger will claim both lives. The daggers were originally owned by the original members of The Brotherhood of the Five, humans spelled by a witch who were supernaturally enhanced in strength, reflexes, and have an instinct to hate and want to kill all vampires even if they die. Although not on par with a vampire, they are enough to fight them more evenly and are highly skilled to hunt and kill vampires. They are the first known owners or creators of the White Oak Ash Daggers, as they knew Original Vampires could not be permanently killed. As they did not know Niklaus was an Original Vampire/Werewolf Hybrid, they were unaware that the silver daggers would not work on Klaus, which led to the original members deaths.
The Original Vampire Kol Mikaelson wanted to make a dagger to work on Klaus as payback for all the times Klaus daggered him. His knowledge of magic showed that he knew how to transform one of the silver daggers into a gold dagger, a dagger that could neutralize Klaus as a magic loophole to his werewolf gene, as he could not replicate the original spell that made the daggers. As Kol was possessing the witch Kaleb, Kol and Davina successfully created a gold White Oak Ash Dagger from a silver White Oak Ash Dagger by using Kemiya magic.
The daggers are known to have existed as early as 900 years before Pilot, back in the twelfth century. The original known owners were the members of The Brotherhood of The Five. It is unknown if the witch who enchanted the daggers was the same witch of The Five, or someone else, but the former is most likely.
Alexander showed Rebekah his dagger and explained that it was a weapon to use against a special kind of vampire (referring to an Original Vampire) and that it would serve as a useful weapon until they could find the cure and permanently kill the Original Vampires. He then plunged it into Rebekah's heart. On the same night the others tried to disable the Originals, daggering all of Rebekah's siblings. However, due to Klaus' dormant werewolf side and the fact that the daggers were made of silver, the dagger didn't work on Klaus. Their plan backfired when the hybrid killed them all in retaliation.
Klaus revived all of his siblings but Finn, and kept the daggers for whenever he wished to impose his will over his siblings. He would use the daggers when in disagreement with his siblings, such as when he daggered Kol in the early 1900's and Rebekah in the 1920's. Keeping the daggers in their hearts kept them neutralized so Klaus kept his daggered siblings wherever he went, resting in coffins until he was comfortable re-awakening them.
One of the daggers ended up in the possession of John Gilbert, who tried to have Damon Salvatore use it on the Original, Elijah, knowing that if a vampire tried to use it on an Original, they'd die from using it. This was discovered though and Alaric Saltzman stabbed Elijah with it instead. However, he was unaware that removing the dagger from the body would revive the Original, Elijah waking shortly afterward. He was stabbed once more, this time by Elena Gilbert, who left the dagger in his body this time. The Salvatores kept Elijah's neutralized body in their cellar but when Elena felt he was the only one who could take on Klaus, she removed the dagger from his body and gave it to him as a peace offering, showing him she did not intend to threaten him again. Klaus broke the curse that prevented him from becoming a hybrid and once he did, daggered Elijah and stored him in a coffin with the rest of his siblings.
Klaus removed the dagger from his sister once he needed her to figure out why he couldn't make successful hybrids. Upon awakening, she stabbed him with the dagger, knowing it wouldn't kill him but hoping it would hurt him, which it did. When Mikael came wanting to hunt down Klaus with a white oak stake he had, the only weapon that could completely destroy an Original, he had Elena dagger him as part of the plan to lure Klaus to him. He was then undaggered once they had set their trap. Shortly after, Elena used the dagger on Rebekah, neutralizing her once more, fearing that she would betray them and aid Klaus. Rebekah was kept in the Salvatore cellar like her older brother, Elijah, had been. When her body was returned to Klaus, he removed the dagger but had then learned that Rebekah was now aware of the fact that Klaus had killed their mother, pushing the dagger into her once she started to awaken, fearing her reaction. The coffins of the neutralized Originals were stolen and after a struggle, returned to Klaus, but Damon had pulled the dagger from Elijah's chest when he returned him, reviving Elijah. Elijah removed the daggers from the rest of his siblings who were far from happy with Klaus. Finn and Rebekah stabbed him with the daggers, knowing they wouldn't neutralize him but would hurt.
After the Originals were linked as one, the Salvatores gave the dagger they had possession of to Alaric Saltzman, who daggered Kol, which neutralized all the Originals but Klaus, who quickly found them and removed the dagger from his younger brother. After Esther had possessed Rebekah, she had Alaric dagger her daughter while she returned to her original body. Once she died, Klaus removed the dagger from Rebekah.
When Klaus thought Rebekah knew too much about the cure, risking their search for it, he daggered her once more. Some time later, her neutralized body was found by April Young who removed the dagger. When Kol discovered the truth about the cure and the ancient immortal Silas, he tried to stop the hunt for the cure and Rebekah threatened to dagger him, which upset him greatly, in disbelief that she would resort to daggering siblings like Klaus did. Kol stole the rest of the daggers from Klaus, with only Rebekah remaining in possession of one, which she eventually gave to Stefan.
In Always and Forever, Klaus used one of the daggers to once again neutralize Elijah, seeing him as a weakness that Marcel could use against him. In truth, he made a deal with Marcel to dagger Elijah and give him his body as a way of being allowed into his inner circle.
Upon Kol Mikaelson's resurrection by possessing the witch Kaleb, Kol reveals that over one hundred years ago, he was working with witches to turn one of the silver White Oak Ash Daggers into a gold White Oak Ash Dagger that would work on Klaus alone. Kol wanted payback for all the times he was daggered, and allied with witches in New Orleans in 1914 to create a dagger to neutralize Klaus. His hope was to free New Orleans, the cities witches, and his siblings from Klaus' dictatorship over everyone and everything. Creating the cursed objects from Season One was practice for his witch allies to then try and transform a silver dagger into the gold dagger by using Kemiya magic, and channeling a perfect paragon diamond. Upon finding a large enough diamond, Kol's witch allies were imprisoned in the Dowager Fauline Cottage to never leave through a boundary spell, and the diamond was taken by Klaus and Marcel Gerard. Kol was daggered after trying to get it back. After getting the diamond back in the present day, Kol and Davina successfully made the gold White Oak Ash Dagger before Kol dies from the death hex his brother Finn placed on the body he was possessing. Before his death, Kol told Davina to keep the dagger to protect herself from Klaus if she needed to.
In When the Levee Breaks, after a devastated Davina and Josh find the body of Aiden, and assume Klaus killed him, Davina gives Elijah the dagger to put Klaus down. Aiden died at Dahlia's hands, but was made to look like Klaus killed him. Klaus took the blame to make others fear him. Elijah and Klaus fought, and Klaus was stabbed with the dagger, successfully neutralizing him for the first time in history by a White Oak Ash Dagger.
Whereabouts
Before the series
Five owned by the Brotherhood. One put in each Original. Removed by Klaus from all but Finn, which is left in him from 1114 to 2012. (The Five)
By this point, one is in Finn, one in Elijah, one in Kol, one in Rebekah, one owned by Mikael and the location of the dagger given to Elijah by Elena is unknown.
Klaus removes Rebekah's dagger, meaning he now owns one not being used. (The End Of The Affair)
Mikael gives his dagger to Elena to use on him. She then uses it on Rebekah. (Homecoming) This means that four are in the Original siblings, one is with Klaus, and Elijah's is unaccounted for.
Elijah removed the daggers from Finn, Kol and Rebekah. They attack Klaus with them. (Bringing Out The Dead)
Damon gives his dagger to Alaric, who uses it on Kol. Klaus removes it and takes it. (All My Children) He now has one, while each of his siblings presumably have theirs, and the one given to Elijah by Klaus is unaccounted for.
Esther gives a dagger (likely Rebekah's or Finn's) to Alaric to stab Rebekah with. Klaus removes it. (Do Not Go Gentle)
Season Four
By this point, Klaus seems to have recovered the daggers left in Finn and Kol, has taken two used on Rebekah, and the one used by Alaric against Kol. The whereabouts of the one given to Elijah by Elena are unknown.
By this point, Stefan owns one, and Klaus has inextricably come to own three, likely reclaiming them after Kol's death. The whereabouts of the dagger that Elena gave to Elijah are unknown. Another dagger seems to be missing, perhaps hidden by Kol.
One dagger is used by Klaus against Elijah. (Always and Forever) Davina accidentally revives Elijah, and he keeps the dagger. (Tangled Up In Blue)
Klaus' other two are stolen by Hayley and given to Rebekah. (Tangled Up In Blue)
Golden Dagger created from Kemiya to neutralise Klaus and him only
Season Two
By this point, Stefan owns one, Elijah owns one, and Rebekah owns two and Davina owns one. One is missing; the one that Elena gave to Elijah.
The gold dagger was used on Klaus in When the Levee Breaks, being the first time Klaus has been neutralized by one of the White Oak Ash Daggers.
Usage
The dagger has to be dipped in the ash of the white oak tree. Then a human has to plunge it into an Original vampire's heart. This will neutralize the original for as long as it remains in the heart.
It is unknown if or not the dagger has to be dipped every time, before it is wielded. Klaus, once, in a fit of rage, pulled out Kol's dagger to kill Elijah but didn't go through with it. It probably wouldn't have worked.
In Girl in New Orleans, Davina pulled the dagger from Elijah's chest, inspecting it before plunging the dagger back. Elijah woke up several hours after. This seems to support that the daggers only work if dipped in White Oak Ash each time.
It is not supposed to be wielded by demons as it would claim both lives - of the Original as well as the demon. It is not yet known what falls under the definition of demon, but normal vampires are known to be included (the word "demon" probably refers only to vampires as the original owners, the five, have only referred to them as demon).
A definitive scene depicting what exactly happens to vampires, when they use it, has not yet been shown. However, it is possible that some vampire must have attempted to use it, which is why the writings suggest that demons mustn't use them.
Apparently, Original Vampires themselves don't seem to be under the definition of 'demon'. Still, Klaus has been the only one who has ever daggered his siblings on screen. It might not affect Klaus for three reasons:
Original vampires were made to protect themselves; nature didn't consider them as demons. Rebekah attempted using the dagger on Kol but she didn't go through with it, so it is unknown what happens to originals other than Klaus when they use it.
Klaus has a werewolf side, so silver based magic never worked on Klaus. Even if other Originals could get neutralized along with the Original they daggered, the same wouldn't affect Klaus. This by extension also means that werewolves can safely dagger an Original.
The Spell that createdthe Originals decreed that only wood from the White Oak Tree can kill them. From this perspective, it would explain why Klaus can safely dagger another Original.
It is unknown what happens if the daggers are used on normal vampires.
It is possible that nothing happens, and they just heal once the daggers are removed, as the spell that enchanted the daggers is only known to be meant for originals.
However, all weaknesses of originals have been generalized in normal vampires (any wood kills vampires as opposed to Originals dying only off of white oak wood). Wood just temporarily disables originals. So, it is possible that the daggers would kill a vampire permanently.
It's unknown whether or not hybrids can use the dagger since the only known ways to kill a hybrid are decapitation and heart removal.
Victims
Elijah (neutralized by Alaric Saltzman, Elena Gilbert, Klaus, and The Five)
Rebekah (neutralized by Alexander, Klaus, Elena Gilbert, and Alaric Saltzman)
Finn (neutralized by The Five, and Alaric Saltzman)
Niklaus (neutralized by Elijah)
Trivia
The daggers strongly resemble the seven "holy daggers" that were featured as the means to kill the Antichrist, Damien, in The Omen film series.
Klaus is shown to threaten his siblings by the threat of silencing them with this dagger,
For now, Rebekah has all the daggers, except one, which is supposedly with Elijah as he is "revived" with the dagger in his chest.
Klaus has all the daggers at first, but he used one on Elijah, and the others were stolen by Hayley who gave it to Rebekah.
Though Klaus is the Original that always daggers the other Originals, none of the daggers is in his possession now. Instead, the daggers are with his undead siblings, Elijah and Rebekah.
Klaus is currently the only Original that has used it on his siblings, Rebekah tried to use it on Kol, but she did not.
Elijah has broken this trend in When the Levee Breaks, as Elijah daggered and neutralized Klaus with the gold White Oak Ash Dagger that was made to exclusively work on Klaus.
Elijah and Rebekah are the most common victims of the daggers.
Though being daggered quite a lot of times, Elijah seems to be daggered for the least amount of time with Kol being daggered at least 100+ years, Rebekah being daggered at least 142+ years & Finn being daggered at least 900+ years. The only exception is Klaus that can't be affected by the dagger and Mikael who is daggered for less than a year, but he is entombed by Abby and daggered by Elena, making him neutralized longer than Elijah.
A reason why Klaus never died from neutralizing his siblings is because of his werewolf lineage.
However, as an original can only truly be killed by the white oak stake it could be possible that unlike non-original vampires they can survive wielding the daggers. Since Rebekah attempted to dagger Kol it seems a rather possible theory.
Kol mentions that the hunters forged the white oak ash daggers and since the brotherhood of five were seen with them in the flashbacks they are presumably the ones who created them while the witches who spelled them are still unknown.
Kol reveals that the spell to create the daggers is impossible to replicate but the element of the daggers can be changed. Example from silver to gold.
Currently there is one gold dagger. Created by Kol and Davina, and currently in the possession of Davina, it is the only thing beside Papa Tunde's blade that can neutralize Klaus.
In When the Levee Breaks, Elijah used the gold dagger for the first time to neutralize Klaus, as he was becoming to dangerous and unpredictable regarding his plan to kill Dahlia and protect his daughter Hope.
