The Satarrans were a humanoid civilization from the planet Sothis III. Although they were not as technologically advanced as the Federation, they possessed a unique device which allowed them to wipe the collective memory of the entire crew of a starship. They also seemed able to manipulate the computer memory banks of a Galaxy-class starship.
By 2368, the Satarrans had been at war with the Lysian race for decades. In that year, the Satarrans attempted to use the USS Enterprise-D to launch a devastating attack against the Lysian Central Command. They used their memory wipe weapon on the crew, placed an operative known as Kieran MacDuff in the first officer position, and planted false orders from Starfleet Command which stated that the Enterprise was to destroy the Lysian headquarters.
Although the crew was unable to restore their full memories by the time they were to attack the Lysian headquarters, Captain Jean-Luc Picard realized that the Lysians posed no threat to the Galaxy-class starship or to the Federation at large (the station, home to 15,311 people, was little more than target practice for the Enterprise, while its entire defensive output would not constitute enough of a threat to bother raising shields), and that the orders must have been falsified. MacDuff's true nature was then revealed, and the Enterprise stood down. (TNG: "Conundrum")
The Satarran head and torso were designed and sculpted by Michael Westmore and Ed French, taking four days to complete the sculpt. For its brief appearance, the head and torso were mounted on a stand, shot frame-by-frame, and inserted optically into the final shot. Westmore considered it "one of the most time-consuming and expensive makeups we've ever done [...], and yet it was only seen for a few seconds". (Star Trek: The Next Generation Makeup FX Journal; Star Trek: Aliens & Artifacts, p.121)