The Koinonians were an ancient, intelligent culture that was native to the Koinonian homeworld.
These physical Koinonians also coexisted on the planet with a Koinonian species that existed as energy forms.
The Koinonians destroyed their own civilization in a series of bitter conflicts between different factions. They lasted for generations, centuries before the 24th century. Those conflicts were later called the Koinonian Wars. They left ruins in underground caverns and only sparse data about the Koinonians survived into the 24th century.
In 2366, the USS Enterprise-D studied the remains of the civilization. Markings in those caverns and subterranean tunnels were identified as Koinonian, thereby making the identification of the planet as their homeworld possible. One room discovered was a large ceremonial chamber, but it was booby-trapped by the Koinonians using advanced explosive devices with subspace proximity detonators. During the away mission, one of these devices exploded without warning, killing Marla Aster. (TNG: "The Bonding")