UFO drivers, ostensibly

• They're stereotypically green
• Sci-fi group
• They might come in saucers, for short
• "Captain Video" figures, for short
• Presumed UFO crew
• Some "X-Files" characters
• Aliens, like the one in a 1982 Spielberg movie: Abbr
• Flying saucer crew, for short
• Alien life forms, for short

Wikipedia Word definitions in Wikipedia
ETS is an abbreviation of: