As far as anyone in the galaxy can figure, the Borg are the original trans-sapient metaspecies. They've kept this going. The Borg, in short, are a networked consciousness that have the goal of improving themselves, and the rest of the universe's sapient species, through biological and mechanical enhancement.
The Borg began as a spaceborne civilization calling itself the Collective.
Tiered organizational structure. Singulum Matrix Sector