Breen

The Breen are a fictional extraterrestrial species in the Star Trek science fiction franchise. They were first mentioned in "The Loss", a fourth season episode of Star Trek: The Next Generation that first aired in 1990. References to them were made in a number of other Next Generation and Star Trek: Voyager stories, but they did not appear until the 1996 fourth season Deep Space Nine episode "Indiscretion". On Deep Space Nine, they played a significant role in the final story arc of that series in 1999, during which much information about them was revealed. The Breen's true appearance remains unrevealed to viewers, as they have never been seen onscreen without their masks.