Kleeya, Idryll woman
The Idryll are an ancient civilization that existed within the Beta Quadrant.
They are a humanoid species who were very advanced and developed the ability to create genetically engineered worker beasts to serve them. However, something happened and the animals, named Exomorphs, turned against their creators. This 'rebellion' of their creations nearly destroyed the Idryll civilization before they managed to shut the animals down. This act effectively removed them from being a spacefaring species and reverted them into a pre-warp civilization.
The Idryll were later culturally assimilated by the Attrexian species who brought them into their society. However, they made sure that all knowledge of the Idryll's history was suppressed but this did not stop several small rebel cabals who defied the Attrexian government.
One such rebel cabal attempted to restart the Exomorphs and succeeded. This group was stopped before their plans came to fruition.
Eventually, the Attrexians admitted that they suppressed the Idryll's research, but it is unknown what happened after that. (TNG video game: Star Trek: Elite Force II)