Leviathan

The ancient apex race in whose likeness the Reapers were made.

The Leviathans are an ancient aquatic race in Mass Effect that dominated the galaxy in the time before the Reapers, and the entity at the centre of Mass Effect 3: Leviathan. Proud and aloof, they regard themselves as the galaxy's first and only apex race and other races as tools meant to serve them, and they can influence lesser-minded organisms to the point of complete physical and mental control, turning them into thralls. Massive and resembling Earth cuttlefish or squid, they are the likeness in which the Reapers were designed. With the advent of the Reapers they were forced into hiding, observing the harvests while erasing evidence of their existence for hundreds of millions of years.