The alien, or Xenomorph, is an extremely lethal breed of extra-terrestrials. Designed by the artist H.R. Giger, they made their first on-screen appearance in Ridley Scotts "Alien" back in 1979, and since then there has been three sequels made. The alien breed by laying eggs containing a parasite that jumps up and infects whoever gets too close with an embryo. This grows in the poor hosts chest until it eventually bursts free, killing the host.