Dragonbinder

Dragonbinder is a mysterious artifact once held by Euron Crow's Eye, passed from him to his brother Victarion in order to claim dominion over the dragons of Daenerys Targaryen. Lost during the Second War of the Conquest, it has since been rumoured to be possessed by the Temple of the Lord of Light in Volantis.

History
The only item of its kind remaining in the known world, the dragon horn called Dragonbinder was supposedly discovered in the ruins of Valyria by Euron Greyjoy some time before 299AC. Upon his return to the Iron Islands and his election as its King, Euron tasked his brother, Victarion Greyjoy, with using the horn to bind the dragons of Daenerys Targaryen to his will.

During his journeys, Victarion discovers a red priest named Moqorro floating in the sea following a wreck, and takes him onto his vessel. Moqorro convinces the Greyjoy that the only way for Victarion to survive the wound he has taken on his arm is for the red priest to heal him, which he does. The crew of the vessel are afraid of the red priest, disliking his calm demeanour and odd ways. Victarion, however, keeps him aboard, and even shows him the dragon horn.

After meeting with Daenerys Targaryen and agreeing to ferry her west back to Westeros, Victarion decided against blowing the horn, hoping instead to win back the Iron Islands from his brother with the use of Daenerys Targaryen and her dragons. Though Moqorro offered to make him the master of the horn, Victarion was not quite ready to trust the foreign priest yet.

Months later, in the fighting outside of Dragonstone, the Iron Victory takes heavy losses attempting to recapture the island. Victarion is wounded, but with the aid of Moqorro manages to survive.

Here, tales differ. Some say that Moqorro used magic upon Victarion and the crew, binding them to his will - others that he used subterfuge and falsehood to convince the Ironborn that his will was in fact Victarion's. Whatever the case, it came to be that Moqorro used the Iron Victory to ferry himself east instead of west, assuring the Ironborn that he could better heal their master if he had access to the markets of Pentos. The jaunt ought have taken a fortnight at most, the red priest assuring them good winds across the sea - but upon arrival in the east, Moqorro disappeared -- along with the dragonhorn, and several of the crew.

From there, Dragonbinder disappeared from the history books, lost to rumour and myth. Until some time in 330AC, rumours began to spread that it was in the possession of the High Priest of Rhllor. There, according to the tales, it remains to this day; as of yet unblown, and as of yet unclaimed.

Abilities
The dragonlords of ancient Valyria purportedly used horns such as Dragonbinder to tame their beasts, though the method and practice of this has been lost since the Doom. It is not known if one horn can control more that one dragon, or how many dragons one horn can control.

Sounding the horn seems to burn a man from the inside out. When sounded in the presence of a dragon, legend tells that the dragon will be bound to the will of the horn's master. Mastery of the horn can supposedly be attained through blood; though the direct method is not known.

Location
Rumour locates Dragonbinder in the vaults of the Temple of the Lord of Light in Volantis, though this has never been confirmed.