Long before Cailee Spaeny took to fighting off Xenomorphs in Alien: Romulus, Sigourney Weaver showed just how terrifying extraterrestrials can be in 1979's Alien. Since hitting theaters 45 years ago, the Ridley Scott classic has earned a reputation as one of the most iconic sci-fi horror flicks in cinema history, a feat that didn't come without creativity, special effects and a whole lot of behind-the-scenes fun. 

From Sigourney Weaver wearing her facehugger on her sleeve to SFX legend H.R. Giger hand-sculpting the Space Jockey, here are 46 pics from the original Alien.