Why did Dumbledore ask Snape to kill him?

Severus Snape: "Are you intending to let him kill you?" Albus Dumbledore: "Certainly not. You must kill me." Severus Snape: "Would you like me to do it now? Or would .... 'I ask this one, great favour of you, Severus, because death is coming for me as surely as the Chudley Cannons will finish bottom of this year's league. read more

Dumbledore wanted Snape to kill him because he felt Snape understood that it was for the best and that way a mere boy like Draco would not have to live with the guilt and horror of having killed someone, while Snape would be able to do it knowing it's what Dumbledore wanted. read more

Dumbledore asked Snape to kill him because he was already a dying man. He knew that his end was near because he had put on the ring Horcrux, which had a powerful curse in it. He actually wanted Snape to be the true master of the Elder Wand, though that did not quite work out. read more