How killd dumbledore?

Answer 1

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.

Answer 2

Dumbledore had put on a cursed ring and had it not been for Snape stopping it from spreading around his body he would have died, however he was going to die within a year. So to make things easier he asked Snape to kill him which would protect Snape's cover and make sure that Dumbledore was the last true master of the Elder wand.

Answer 3

Draco Malfoy, but he was not able to commit the murder, it was Severus Snape who killed Dumbledore.

Answer 4

Draco Malfoy in the Astronomy tower.