Tkon
From Star Trek : Freedom's Wiki
Tkon are a humanoid species who once established the Tkon Empire which stretched across the Alpha and Beta Quadrants. The empire suffered an unknown fate and billions of the Tkon were killed. Very little remains of their once great civilization.
In 2414, the USS Boudicca and the USS Rosenante investigated a Borg presence at Dovek II which was a planet known to have been part of the Tkon Empire. When the Borg opened a temporal conduit both starships followed and as a result were able to observe for a short time the culture of the Tkon near the end of their empire.
The Tkon first appeared in the joint USS Boudicca and USS Rosenante mission Once More Into The Breach