Dumbledore allowed Snape to kill him, thus destroying the Elder Wand's power, when it was already assured Voldemort couldn't kill Harry.

Gandalf, a Maiar, guided Aragorn and Bilbo on their respective quests to unite Gondor and take down Smaug.

Obi-Wan allowed himself to be killed by Vader, thus spurring Luke permanently against him, turning into the most potent weapon for the Rebel Alliance ("more powerful than you could possibly imagine," indeed).

I just posted the image here because I saw it making its rounds via FB, but the references are solid enough (even if everyone did die in some way or another).

Doc Brown wasn't bearded…