Xenomorph or Alien is a fictional endoparasitoid extraterrestrial species that is the eponymous antagonist of the Alien film series.
A figure appears in Helter Shelter.
Treehouse of Horror
In Treehouse of Horror XXI, When Professor Frink walks in front of his X-ray machine, an Alien embryo is seen inside him.
an Alien is among the movie creatures and characters seen in the field next to the Simpsons' house, in the opening of Treehouse of Horror XXIV.