Douwd

The Douwd are an immortal species which can assume any physical appearance, although in their true forms, they resemble translucent energy-based humanoids. They have the power to create elaborated illusions and to annihilate entire civilizations with their minds. Fortunately, however, the only known member of this species has a very strong code against killing - although in a moment of unexpected grief and anger he destroyed the Husnock to avenge the death of his Human wife.

Appearances

 * Star Trek: The Next Generation, s03e03, "The Survivors" (1989)