Hurq, a Klingon word meaning "Outsider" made an attempt about 1500 CE to conqueror the Klingon Home world. That did not work well for them. The Klingons seized the ships the Hurq landed in, after fighting like mad to drive them off, reverse engineered the technology and went Hurq hunting.
The Orions who had dealt with the Klingons in the past had always made sure to keep the aggressive race down on the farm so to speak. Now they were out in space and in a fighting mood. It took a century to back track the Hurq and destroy them. They went far afield and many of the battle fleet never saw home.
By the time it was over the Hurq were extinct.
Recent interphase events have returned two Hurq to the present. They are now just critically endangered.
Hurq are mammals. Under extreme biological stress, they can change gender by consuming a common cooking spice in the Klingon Empire. The whole plant, not just the seeds.