Sovereign (Mass Effect)

Sovereign (also known as Nazara) is the true villain in Mass Effect, a member of an ancient race of evil, sentient starships called the Reapers who want to assimilate all the other organic life in the galaxy. He is controlling Saren Arterius, and wants him to find the portal called "The Conduit" which will allow Sovereign and his fleet to launch an attack on the Citadel. He is known for his tremendously deep and intimidating voice, which was provided by Peter Jessop.

Because he is thousands of feet in size, Sovereign is not directly fought as a boss in the game, but is fought indirectly at the end where he takes direct control over Saren's corpse during the final battle, right after which he is destroyed by the Citadel fleet while trying to finish activating the Conduit.