A long-dead race that ruled most of the galaxy a billion years ago and left behind stasis boxes containing priceless and sometimes deadly artefacts.
The Slavers are an extinct species described in the animated episode The Slaver Weapon, adapted by Larry Niven from one of his own short stories. A billion years ago they controlled most of the intelligent life in the galaxy, until a revolt led to a war that destroyed the Slavers and their subjects alike.
Their only relics are stasis boxes, containers in which time does not pass. One such box once yielded the secret of artificial gravity used in starships, and boxes can be used to detect one another.
Spock, Sulu and Uhura are carrying a stasis box aboard a shuttlecraft when Kzinti raiders lure them to an ice world and seize it. Inside is a shape-changing hand weapon that once belonged to a Slaver spy, including a setting of terrible destructive power. The weapon finally destroys itself and its captors.