Thanos' snap turned heroes to dust in Avengers: Infinity War - but seeing as the effect of his attack was random, he only technically, physically killed two good guys himself: Gamora and Vision.
Although he could have killed all of the Avengers in his quest for the stones, he didn't. Even though the reason why he didn't is obvious, Marvel Studios' Head of Visual Development Ryan Meinerding has spelled it out for you.
"The plan of getting all the Infinity Stones is putting [Thanos] in the position of being so powerful that he is sort of calmer, more single-minded, and more reasonable," he said in The Art of Avengers: Infinity War (via ComicBook.com).
"He is not necessarily worried about killing the heroes. As long as he ends up with the stones, he can accomplish what he wants to."
Avengers 4 will (likely) see the heroes undo all of the damage caused by Thanos, bringing all of your favourites (and Mantis) back to life.
