Alien (1979)

Ridley Scott's sci-fi horror stripped away every reassurance the genre had offered and replaced it with the inescapable terror of being hunted in a sealed space with no exit. H.R. Giger's biomechanical creature design — genuinely disturbing rather than conventionally monstrous — combined with Scott's insistence on practical effects created a film whose set pieces, including the chest-burster scene, provoked genuine shock from cast and audience alike. It won the Academy Award for Best Visual Effects and spawned one of cinema's most enduring franchises.