Leviathan

The Leviathans are an ancient aquatic race that dominated the galaxy in the time before the Reapers. Proud and aloof, they regard themselves as the galaxy's first and only apex race, and think of other races as mere tools meant to serve them. With the advent of the Reapers, the Leviathans were forced into hiding to preserve themselves, and were content to observe the Reapers' harvests while surreptitiously erasing any evidence of their existence over the course of hundreds of millions of years.