Astonishing X-Men #4
"Gifted: Part 4"
By Joss Whedon and John Cassaday
It was obvious right from the start that Joss Whedon's run on the X-Men was going to be a special one; it fit perfectly with his previous work, mainly due to his ability to transform Kitty Pryde into a Buffy parallel at every turn. The moment that he cemented his place in X-Men history, however, was when, at the end of the fourth issue of his series, he brought a character back from the dead in a spectacular curve-ball move.
Expecting to find a resurrected Jean Grey hidden in the bowels of a mysterious laboratory, Kitty Pryde found herself confronted with her long-dead boyfriend, Colossus. In a beautiful, silent moment he ran right through her and proceeded to battle the enemies in the depths, while she stood still, trying to absorb the reality of the situation. The scene is made only more emotional when Colossus breaks down in front of her, praying that he has finally died after years of torture at the hands of his oppressors.
Colossus, of course, died to save the world from the deadly Legacy Virus, injecting it into himself in order to disperse it throughout the planet. His return was completely unexpected and proved to be one of the defining moments of Whedon's run and the start of his true arc for Kitty Pryde, as she and Piotr found themselves drawn to each other once more.