The Shadow Spire, also known as just the "Shadow" are the most mysterious offshoot of the Spire race known to humanity. They were an ancient branch of the species that fled from the Andromeda galaxy to the Milky Way several thousand years before the game's events. The Shadow were the creators of the Shadow Drive, the Shadow Vessels, also known as Champions, and given the similarities in their design, they probably were the original creators of the Tackle Drone Launcher and the Saboteur.
The only presence the Shadow Spire have in the game is in the form of the Shadow Vessel/Champion, a nearly indestructible starship that can learn and grow stronger. Given the fact that most Spire are ship-sized creatures, and the Shadow were Spire, their ship/bodies were probably similar to the Shadow Vessel's default appearance, an olive green starship with long "wings".
Role in AI War
In the Nebulae scenarios added by Ancient Shadows, the Champions have a vital importance in helping the friendly factions defeat their enemies, leading all the way to a Shadow planetary "adjustment" device which can be used to heal the damage Earth suffered at the hands of the AI.