Answer
The exact curse was never specified, but it was caused by him wearing a cursed ring.
Answer
Avada Kedavra, cast by Severus Snape. But he was already poisoned and cursed, so he would have died soon anyway.
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because apparently it could return the dead -i think he wanted his sister, Ariana or something like that to return-but that's just my guess
No, Dumbledore does not have a horcrux but Voldemort has 7. Horcruxes are described as one of the foulest forms of Dark Magic. That is not the sort of thing Dumbledore would use.
The ring he had on was Voldemort's horcrux so it had a curse on it. When Dumbledore tried it on, Dumbledore got the curse
Put a curse on his hand that would soon spread to the rest of his body and kill him.
SpoilersSnape kills Dumbledore with avada kedavra. It is later revealed that this is what Dumbledore wanted as he was already dying after being cursed by a horcrux.
None of the Defense Against the Dark Arts teachers ever lasted more than a year as the job was cursed.
This is a very broad question, and not worded correctly. Severus Snape killed Albus Dumbledore in the end of the sixth book. Dumbledore had asked Snape to kill him, to save Draco Malfoy's soul because of the Unbreakable Vow that Narcissa Malfoy made Snape take in the beginning of the sixth book since Voldemort had ordered Draco to kill Dumbledore.
Dumbledore's full name is Albus Percival Wulfric Brian Dumbledore, giving him three middle names.
Albus Percival Wulfric Brian Dumbledore and his brother was called Aberforth Dumbledore He also had a sister called Ariana Dumbledore.