In ufology, Greys, also known as Roswell aliens, Zetas, an Reticulians, are aliens or extraterrestrial life forms that appear in purported modern-day encounters and other UFO-related paranormal phenomena. Said to be one of several species of aliens, greys make up approximately 75 percent of all aliens reported in the United States, 20 percent of all aliens reported in Continental Europe, and 12 percent of all aliens reported in Great Britain.