One of the greatest sci-fi films of all time, and one of the greatest horror films of all time, Alien pretty much stands alone as a movie equally as influential in one genre as it is another. Famously pitched as "Jaws in space", the opening hour trades in Jaws-esque atmosphere and mood to set up what is a riotous, thrilling second half. Starting with the infamous Chestbuster (see above), and onto the Xenomorph's big reveal, Alien is a masterclass in suspense and pay-off. Held together by Sigourney Weaver's dogged turn as Ripley, Alien is part monster-movie, part sci-fi space adventure, and wholly magnificent. A film more than just a some of its iconic parts, Alien is a film that weaves all of its strands together to create a near-perfect tapestry. Perhaps the most influential entry on this list other than Psycho, films - both horror and not - have attempted to replicate Alien's unique blend of materials ever since, often failing because they don't understand that Alien itself is a blend of its own influences - a touch of 2001 here, a dash of Jaws there, a splash of Howard Hawks' The Thing. What sets it apart, however, is that where most films replicate the feeling of an influence, Alien replicates the thinking of an influence, then building on it and expanding it to create a whole new set for itself.
