The Obsidians are an ancient race of aliens, made up of numerous genetically engineered speices. No one knows exactly how old they are, or where precisely they came from. They are like interstellar locusts, travelling from planet to planet and stripping it bare of everything useable, leaving behind nothing but blackened and lifeless rocks. They travel between solar systems in enormous, city sized "Blade ships". The social structure of the Obsidians is based on the various types of creatures. From lowest to highest, this is the order:

Soldier creatuers:
Imp (Cannon fodder)
Splicer (Basic infantry)
Reaver (Heavy infantry)
Thresher (Assualt troops)
Titan (Heavy assault troops)
Chameleon (Assassins/Ambush Can become almost totally invisible)
Spectre (Sniper)
Hunter (Overlord and Hive Queen bodyguards)
Harpy (Air/Space Superiority Fighter pilot)
Reaper (Heavy bomber pilots)

Command Creatures:
Fury (Harpy flight leader)
Banshee (Elite Fury pilots)
Jackal (Lieutenant)
Deamon (Captain)
Revanent (Commander)
Overlord (General/Admiral)
Hive Queen (Head of all Obsidians)