Sovereign

The Sovereign is a gigantic vessel of almost unimaginable power and sophistication, which serves as the flagship for the rogue Specter Saren. A vanguard of the Reapers left behind to instigate their eventual return from black space, it has spent the last 50,000 in a state of near-constant hybrination, awakening only on a periodic basis to assess the status of sentient organic life. In order to further its own ends, it struck a deal of Saren, who took the great machine as his flagship, only to later fall -- like so many others -- under the dominating effects of Sovereign's Indoctornation. Primarily working through a series of thralls, it was the duty of the squid-like spaceship to bring about the end of the Cycle, and serve as harbinger for the return of its kin. During gameplay, it was first introduced during the surprise attack on Eden.

This Reaver was destroyed in the final, climactic battle around the Citadel, by the combined forces of the remaining Alliance ships and the human fleet. Perched on top of the Council tower, it was attempting to override the anti-Reaper safeguards put in place by the long-dead elite Prothean science team from Iilos. During this selfsame conflict, it created an avatar through the mechanical implanets in Saren's cadaver, and entered a brief but chaostic struggle with Commander Sheppard and his allies. Upon the destruction of that avatar, and under constant bombardment by a full armada of starships, Sovereign was obliterated, overting the rapid transport of the full Reaper fleet from beyond the galactic rim, and saving sentient life from utter destruction.