TedStixon

Answer: When we see him unmasked as a child, he looks sort of shocked but also vacant - he's staring off into nothingness... this was the moment when he lost his mind and became evil. I think the look on his face was meant to convey that he had simply snapped and was no longer "there." When he's unmasked as an adult, he didn't really look angry to me... he simply looked empty and expressionless. I think it's meant to show that he's no longer really a person... he's totally gone. There's nothing left but almost instinctive evil.

TedStixon

Answer: In a meta "behind the scenes" context, Michael was more or less intended to basically be the pure, simple personification of evil. He's basically the closest thing there could be to a "real life boogeyman." Choosing not to have him speak was a way for the filmmakers to keep his evil "pure" and simple. He has no real personality or motivation - he simply does evil things for the sake of doing them. His actions speak for him, so to speak. It is also arguably frightening to imagine why someone who could speak would choose not to. In terms of the movies themselves, it's never really 100% explained. It's implied that he stopped speaking and basically lost all traces of humanity after killing his sister. The closest we get to any sort-of direct explanation is in the 2018 sequel that "Halloween" creator John Carpenter approved and produced, in which Dr. Sartain clarifies that Michael can speak, but simply chooses not to for reasons unknown.

TedStixon

Answer: The movie doesn't provide any reason why he targets the three girls, which I think is a wise decision, but you can interpret that Myers chose those three because of Annie's "Speed kills!" wisecrack. It was enough to get him to stop the car. Good enough reason as any.

Answer: (1) In the context of the movie, no. Michael is, as Loomis puts it, "purely and simply evil." He pretty much picks the girls as a target seemingly at random after Laurie drops the keys off at the Myers house. While future movies tried to provide him with a reason (such as saying Laurie is Michael's sister in "Halloween 2"), in this movie, it's pretty much just because Michael is a psychopath and they just so happened to become his target. That's part of what makes him so scary in this film. (2) The mask was picked by the filmmakers because it was the most unsettling. (A clown mask was also considered.) It also had the added bonus of having a vacant, emotionless face that also happened to reflect Michael's vacant, emotionless state. (3) Michael is a psychopath and simply decides to kill all of the girls and save Laurie for last for reasons unknown.

TedStixon

Answer: The only answer given in this film is that Myers is purely and simply evil. He's just doing it because he's compelled to, and doesn't seem to have any trace of humanity left inside of him. Future sequels attempted to give an explanation, but to varying degrees of success. But as far as this original film is concerned - he's just pure evil.

TedStixon

Answer: The movie doesn't require a back story, although subsequent sequels, and the Rob Zombie remake address your questions. Then again, what makes any serial killer kill? The topic has been studied by psychologists for decades. Often serial killers lead normal lives, at least in public.

rswarrior