The stereotypical Grey-skinned Alien (although they might also be green), with big, solidly black, almond-shaped eyes, scrawny body, and disproportionately big, teardrop-shaped bald head. Thought to hail from Zeta Reticuli in U.F.O. conspiracy circles.
In 1947, there was a crash-landing of an Unidentified Flying Object in Roswell, New Mexico. While the government stated the craft to be a weather balloon, some people beleive it was an Honest-to-God flying saucer piloted by an Honest-to-God little green man. The craft and pilot were supposedly taken to Groom Lake Air Force base in Nevada, also known as Area 51.
Greys are usually depicted abducting people (and/or Cattle) and giving them an unscheduled and forceful colonoscopy and/or exploratory surgery.