Why did Severus Snape kill Albus Dumbledore?

Answer 1

Dumbledore put a cursed ring on his hand which would have killed him had Snape not stopped it. Snape told Dumbledore he only had about a year left to live and Dumbledore knew that Voldemort was plotting his death but didn't want Draco Malfoy's soul to be damaged by this. He also knew that Voldemort would want the Elder wand and that Snape needed to keep convincing Voldemort he was on his side.

So, Dumbledore told Snape to kill him which meant Voldemort trusted him, Draco kept his soul intact and Dumbledore died as the last true owner of the Elder wand - although because Draco disarmed him before he died that part of the plan didn't work.

Also because Dumbledore says that he would rather be killed by Snape than one of the other Death-Eaters, such as Belatrix Lestrange who, as Dumbledore put it 'like to play with their food'.

Snape also made an unbreakable vow to Narcissa (or Cissy) Malfoy, to help Draco in his deed set by 'The Dark Lord', and if it should seem Draco would fail, he commit the deed himself. (The deed being to kill Albus Dumbledore)

Answer 2

if you have read the deathly hollows book it explains why. the ring that he had in the order of phoenix on his desk was a horcrux and he had destroyed it causing it to curse him which the curse was for him to die so he told snape to kill him since he was going to die.

Answer 3

At the end of the seventh book when Harry looks in to Snape's memories he finally understands that Dumbledore had asked Snape to kill him. When Dumbledore came back to Hogwarts after finding Marvolo Gaunt's ring, which Voldemort had made into a Horcrux, he was badly cursed--by, as it happens, an incurable curse. Snape tells Dumbledore that he's contained the curse for then in Dumbledore's arm, but it can't last that way forever--Dumbledore will be killed byt he curse eventually. Dumbledore asks Snape how long he has to live, and Snape tells him he might have a year left. This, then, is during the summer between Harry's fifth and sixth years at Hogwarts. Dumbledore then tells Snape that Snape will have to kill him, because killing him would be more merciful than letting him be consumed by the curse of the Horcrux. So Dumbledore would rather be killed by Snape than by the curse; but another reason he told Snape to do it is because he knew that Voldemort was trying to have Draco Malfoy kill him, but Dumbledore didn't want Malfoy to become a killer. After all, Draco was still young and he also had the advantage of being able to change sides. He didn't have to end up like his father, whereas Snape was in it for good as Dumbledore's spy.

Answer 4

Dumbledore knew he was old and needed to die. He prepared presents for the golden trio about Horcruzes and Deathly Hallows. He told Snape, “I am ready to die.” Snape didn’t want to kill him but Dumbledore said that Snape was the one who had to. When Snape saw Draco about to kill Dumbledore, he ran up and killed Dumbledore like he asked.

Answer 5

snape agreed to kill dumbledore because dumbledore was already dying because he wore tom riddle's (lord voldemort) cursed ring

Answer 6

So that Snape could pretend to be a loyal Death Eather.