What makes Alien such a classic? Is it the iconic monsters? The story? The way it was shot? Sure, it's all of those. But there's also another reason it became a classic in the '70s — and it's not one of the reasons we still think of today.
Not only was Tom Skeritt the obvious "hero" in the movie, but Sigourney Weaver's Ripley was a character type that was edgy in 1979 (and arguably to this date, though more widely accepted in SF movies than in other genres and in the real world): she was the kind of woman a certain generation might call "mouthy" or a "ball-breaker". She's a stickler for rules; she's disliked, disrespected and disobeyed by her crewmates; she doesn't scream or cower (nothing against Veronica Cartwright's Lambert; just that there's a reason there's a horror film archetype called the "scream queen"). To be fair, even if Ripley had been cast with a male, the anal-retentive guy is supposed to get it in the last reel of a horror film, having proven he's not really such a huge asshole after all.
Ripley, a brash and (by the standards of the era) unwomanly woman prevails. Without compromising. And the brave, bearded manly-man? Turns out to be a likeable but incompetent dweeb who gets his halfway through the film. Younger audiences just don't get how groundbreaking that was when Alien came out. The movie defied convention, broke not just the rules but social mores that were still popular, and created archetypes that people take for granted these days.
And that's why it's a classic. People seem to think it's the brilliant art design or something. No. It's because it's a rebel movie.
What do you think? Give us your thoughts on just why Alien became a science fiction classic in the comments.