Appears in: Alien (1979), Aliens (1986), Alien 3 (1992), Alien Resurrection (1997), Alien vs. Predator (2004), Aliens vs. Predator: Requiem (2007), Prometheus (2012)*
Scariest moment: Looking for the crew's cat, Jonesy, engineering technician Brett (Harry Dean Stanton) doesn't realize that the fully formed Xenomorph is standing right behind him. The stunned look in Jonesy's eyes are all viewers need to understand the gory fate that Brett suffers once he sees it.
Weakness: Female military officers with short haircuts.

Hands down, the most memorable scene in Ridley Scott's seminal sci-fi/horror classic Alien is also one of cinema's all-time greatest shock moments: Nostromo executive officer Kane (John Hurt), having recently been face-hugged by a small crab-like alien, suddenly starts convulsing at the spaceship's dinner table, before his chest bursts open and a tiny E.T. slithers across the floor.

What Alien's chestbuster rapidly becomes is the film's scariest attribute. Known as the Xenomorph, the tall, lanky bastard—armed with a little fang-filled head inside its bigger mouth—is a truly awe-inspiring creation, one that comes from the mind of Swiss artist H.R. Giger and has yet to be matched in its nightmarish beauty.

[*Cameo appearence.]