It's hard to imagine a more iconic space monster than the so-called Xenomorph from Ridley Scott's 1979 Alien. The design of the creature was made specifically to evoke feelings of horror and sexuality. In fact, Fox was hesitant to let the designer, surrealist artist H.R. Giger, work on the movie because they thought his designs would be too disturbing for audiences.
The costume was built using some rather strange materials. They used plasticine, parts from a Rolls-Royce motor, real vertebrae from dead snakes. Ironically, they also used latex and K-Y jelly, which ties nicely with the sex undercurrent that runs throughout the Alien franchise. The K-Y jelly was used not just to make the costume seem slimy, but also for the creature's saliva.
Still, despite the horror that the design inspired, there was still a man underneath. A casting director saw a Nigerian design student named Bolaji Badejo while he was out for a drink in a bar. Badejo was 7'2", which was perfect for the dimensions they wanted the alien to be. They made a full plaster of his body and created the costume around it. He also attended t'ai chi and mime classes to create better movements for the alien.