A species that wiped the memories of the Enterprise-D crew and planted an agent among them to trick the ship into attacking their enemies.
The Satarrans are a humanoid species at war with the Lysian Alliance. Lacking the strength to win alone, they devised a plan to turn a Federation starship into a weapon on their behalf.
In the episode Conundrum, a Satarran ship scanned the Enterprise-D and erased the memories of everyone aboard. A Satarran agent posing as a human, Commander Kieran MacDuff, joined the confused crew as their first officer and altered the ship's records to make it seem that they were at war with the Lysians. After the ship had already fought Lysian vessels, Captain Picard grew uneasy with orders to destroy a far weaker enemy and refused to continue, and Worf stopped MacDuff when he tried to force the attack through.