Conceived by Swiss artist H.R. Giger, the alien Xenomorph is hands down the king of cinema alien depictions, likely to never be out done. Xenomorphs are scary, lethal, vicious, unrelenting, and thoroughly disgusting in all stages of development, and there are many. Their lifecycle is well-developed: from slimy cocoon, to facehugger, to gestating parasite, to full-sized adult, and beyond (an egg-laying Queen). With razor-sharp claws, acid blood, a set of fanged mouths, and a razor-tipped tail, Xenomorphs are the stuff of nightmares.