Husnock

"Your colony was attacked by a warship–"

"Belonging to the Husnock. A species of hideous intelligence. Knew only aggression... destruction.

- Jean-Luc Picard and Kevin Uxbridge

The Husnock were a species destroyed in 2366 by a Douwd who had assumed the Human identity of Kevin Uxbridge. Uxbridge described the Husnock as being extremely violent and having a destructive nature. He called them "a species of hideous intelligence who knew only aggression and destruction." Their physical appearance is unknown.

The event which precipitated the annihilation of the species was that in 2366 a Husnock warship attacked and destroyed a Federation colony at Delta Rana IV. Unknown to the Husnock, an energy lifeform known as a Douwd was also living on the planet in the guise of Uxbridge. In a split-second of anguish over Rishon's death, the normally-pacifist Douwd destroyed every member of the Husnock race with its enormous powers. The Husnock numbered fifty billion at the time. (TNG: "The Survivors")

"The Survivors" remains the Husnock's sole appearance in Star Trek. No Husnock were seen in the episode and the Delta Rana warship has been debated as possibly not even being a real Husnock vessel, given Kevin's power to create "illusions and false surroundings."